diff --git a/DESCRIPTION b/DESCRIPTION
index 501e2cf..7b146d3 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -20,6 +20,7 @@ Encoding: UTF-8
 Roxygen: list(markdown = TRUE)
 RoxygenNote: 7.2.3
 Imports: 
+    cli,
     DBI,
     dbplyr,
     dplyr,
@@ -29,7 +30,8 @@ Imports:
     lobstr,
     lubridate,
     magrittr,
-    patchwork,    
+    patchwork,
+    pillar,
     purrr,
     rlang (>= 0.4.11),
     RSQLite,
diff --git a/NAMESPACE b/NAMESPACE
index de7b903..dcda475 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -15,9 +15,10 @@ S3method(glimpse,grouped_cg_df)
 S3method(glimpse_experiment_data,cg_tbl)
 S3method(glimpse_metadata,cg_tbl)
 S3method(group_by,cg_tbl)
-S3method(print,cg_skl_tbl)
-S3method(print,cg_tbl)
-S3method(print,grouped_cg_df)
+S3method(summary,cg_tbl)
+S3method(summary,grouped_cg_df)
+S3method(tbl_format_footer,cg_tbl)
+S3method(tbl_sum,cg_tbl)
 S3method(ungroup,grouped_cg_df)
 export("%>%")
 export(":=")
@@ -59,6 +60,8 @@ importFrom(dplyr,group_by)
 importFrom(dplyr,group_data)
 importFrom(dplyr,ungroup)
 importFrom(magrittr,"%>%")
+importFrom(pillar,tbl_format_footer)
+importFrom(pillar,tbl_sum)
 importFrom(rlang,":=")
 importFrom(rlang,.data)
 importFrom(rlang,as_label)
diff --git a/R/check_metadata.R b/R/check_metadata.R
index b9c5169..dd8b910 100644
--- a/R/check_metadata.R
+++ b/R/check_metadata.R
@@ -29,5 +29,27 @@ check_metadata <- function(x, cg_skeleton = NULL) {
     )
   }
 
+  ### metadata should not have duplicated ids ###
+  if (!is.null(ids_column_name)) {
+    stopifnot(
+      {
+        n <- NULL # suppress global binding note
+      "Invalid metadata: IDs are repeated" =
+        xx <- x %>%
+        dplyr::group_by(
+          dplyr::across(
+            dplyr::all_of(
+              c(ids_column_name)
+              )
+            )
+          ) %>%
+        dplyr::tally() %>%
+        dplyr::pull(n)
+
+      all(xx < 2) == TRUE
+      }
+    )
+  }
+
   return(TRUE)
 }
diff --git a/R/new_chronogram.R b/R/new_chronogram.R
index 93c0ea6..bde0ccd 100644
--- a/R/new_chronogram.R
+++ b/R/new_chronogram.R
@@ -1,6 +1,6 @@
 #' new chronogram
 #'
-#' @param x a tbl, a daughter of a join between a cg_skl_tbl and
+#' @param x a tbl, a daughter of a join between a chronogram skeleton and
 #'   one (or more) objects coerced to a tbl.
 #' @param metadata_cols the column names from the metadata tibble
 #' @param ... passed to `new_tibble()`. Adds grouping support.
@@ -17,8 +17,8 @@ new_chronogram <- function(x,
                            metadata_cols,
                            ...) {
   stopifnot(
-    "provided object does not inherit cg_skl_tbl class" =
-      inherits(x, "cg_skl_tbl")
+    "provided object does not inherit tbl_df class" =
+      inherits(x, "tbl_df")
   )
 
   stopifnot(
@@ -29,11 +29,6 @@ new_chronogram <- function(x,
   ## Set first class to cg_tbl ##
   class(x) <- c("cg_tbl", class(x))
 
-  ## remove the cg_skl_tbl class ##
-  class(x) <- class(x)[
-    !grepl(class(x), pattern = "cg_skl_tbl")
-  ]
-
   ## remove the col_ids from metadata column names ##
   col_ids <- attributes(x)$col_ids
   cols_metadata <- metadata_cols[
diff --git a/R/new_chronogram_skeleton.R b/R/new_chronogram_skeleton.R
index 9a86333..22adc80 100644
--- a/R/new_chronogram_skeleton.R
+++ b/R/new_chronogram_skeleton.R
@@ -9,7 +9,7 @@
 #'  rlang::enquo(an_unquoted_string)
 #' @param ids_col provided as rlang::enquo(an_unquoted_string)
 #'
-#' @return x a tibble with class cg_skl_tbl
+#' @return x a tibble with attributes to identify `calendar_date_col` and `ids_col`.
 #'
 #' @seealso [chronogram::chronogram_skeleton()]
 #'
@@ -55,7 +55,5 @@ new_chronogram_skeleton <- function(x,
 
   attributes(x) <- attributes_x
 
-  class(x) <- c("cg_skl_tbl", class(x))
-
   return(x)
 }
diff --git a/R/print_chronogram.R b/R/print_chronogram.R
index 28c6345..41c2648 100644
--- a/R/print_chronogram.R
+++ b/R/print_chronogram.R
@@ -1,130 +1,66 @@
-#' print chronogram
+#' Add a line to tbl header when printing a chronogram, or a grouped chronogram
 #'
-#' @param x a chronogram object (class tbl_chronogram)
-#' @param ... additional arguments passed to tibble print S3 generic
+#' @param x a chronogram, or a grouped chronogram
+#' (class tbl_chronogram or grouped_cg_df)
+#' @param ... passed to [pillar::tbl_sum()]
 #'
 #' @return print to console
-#' @examples
-#' \dontrun{
-#' ## a 3-person chronogram_skeleton ##
-#' small_study <- chronogram_skeleton(
-#'   col_ids = elig_study_id,
-#'   ids = c(1, 2, 3),
-#'   start_date = "01012020",
-#'   end_date = "10102021",
-#'   col_calendar_date = calendar_date
-#' )
 #'
-#' ## Create a tibble containing some metadata for our 3 individuals ##
-#' small_study_metadata <- tibble::tribble(
-#'   ~elig_study_id, ~age, ~sex, ~dose_1, ~date_dose_1, ~dose_2, ~date_dose_2,
-#'   1, 40, "F", "AZD1222", "05/01/2021", "AZD1222", "05/02/2021",
-#'   2, 45, "F", "BNT162b2", "05/01/2021", "BNT162b2", "05/02/2021",
-#'   3, 35, "M", "BNT162b2", "10/01/2021", "BNT162b2", "10/03/2021"
-#' )
-#'
-#' ## Set appropriate metadata column classes ##
-#' library(dplyr)
-#' small_study_metadata <- small_study_metadata %>%
-#'   mutate(across(c(sex, dose_1, dose_2), ~ as.factor(.x)))
-#'
-#' small_study_metadata <- small_study_metadata %>%
-#'   mutate(across(contains("date"), ~ lubridate::dmy(.x)))
-#'
-#' ## Make a chronogram ##
-#' small_study_chronogram <- chronogram(
-#'   small_study,
-#'   small_study_metadata
-#' )
-#'
-#' ## print, with default tibble options ##
-#' small_study_chronogram
-#'
-#' ## print, with eg 3 rows ##
-#' print(small_study_chronogram, n = 3)
-#' }
+#' @importFrom pillar tbl_sum
+#' @seealso [summary()]
 #' @export
-print.cg_tbl <- function(x, ...) {
-  calendar_date <- attributes(x)$col_calendar_date
-  ids_column_name <- attributes(x)$col_ids
-  version_number <- attributes(x)$cg_pkg_version
-  windowed <- attributes(x)$windowed
-  meta <- attributes(x)$cols_metadata
-
-  zz <- NULL # suppress no visible binding warning
-
-  over_min <- x %>%
-    dplyr::group_by(
-      dplyr::across(
-        dplyr::all_of(ids_column_name)
-      )
-    ) %>%
-    dplyr::summarise(zz = (dplyr::n())) %>%
-    dplyr::pull(zz) %>%
-    min(., na.rm = TRUE)
+#' @noRd
 
-  over_max <- x %>%
-    dplyr::group_by(
-      dplyr::across(
-        dplyr::all_of(ids_column_name)
-      )
-    ) %>%
-    dplyr::summarise(zz = (dplyr::n())) %>%
-    dplyr::pull(zz) %>%
-    max(., na.rm = TRUE)
-
-  cat(
-    ## use paste to prevent cat re-formating dates
-    paste(
-      "A chronogram:\n",
-      "Dates column: ", calendar_date, "\n",
-      "IDs column:   ", ids_column_name, "\n",
-      "Starts on:    ",
-      min(x %>% dplyr::pull(calendar_date)), "\n",
-      "Ends on:      ",
-      max(x %>% dplyr::pull(calendar_date)), "\n",
-      # "Spanning:     ",
-      # max(x %>% dplyr::pull( calendar_date )) -
-      #   min(x %>% dplyr::pull( calendar_date )),
-      # " days\n",
-      "Contains:     ",
-      x %>% dplyr::pull(ids_column_name) %>%
-        factor(.) %>% nlevels(.),
-      " unique participant IDs\n",
-      "Windowed:     ", windowed, "\n",
-      "Spanning:     ",
-      over_min,
-      "-",
-      over_max, "days [min-max per participant]\n",
-      "Metadata:     ",
-      paste(meta, collapse = ", "), "\n",
-      "Size:         ",
-      rlang::parse_bytes(
-        as.character(
-          lobstr::obj_size(x)
-        )
-      ), "\n",
-      "Pkg_version:  ",
-      version_number, "[used to build this cg]\n\n"
-    )
-  )
-  NextMethod(x, ...)
+tbl_sum.cg_tbl <- function(x, ...) {
+  default_header <- NextMethod()
+  c(default_header, "A chronogram" = cli::col_blue("try summary()"))
 }
 
+#' Add a line to tbl footer when printing a chronogram, or a grouped chronogram
+#' @importFrom pillar tbl_format_footer
+#' @param ... passed to [pillar::tbl_format_footer()]
+#' @export
+#' @noRd
+tbl_format_footer.cg_tbl <- function(x, setup, ...) {
+  default_footer <- NextMethod()
 
+  meta <- paste(attributes(x)$cols_metadata, collapse = ", ")
 
+  extra_info <- paste(
+                      cli::col_yellow("Dates:"),
+                      attributes(x)$col_calendar_date,
+                      "    ",
+                      cli::col_yellow(cli::symbol$star),
+                      cli::col_yellow("IDs:"),
+                      attributes(x)$col_ids)
 
-#' @export
-print.grouped_cg_df <- function(x, ...) {
-  groups <- dplyr::group_vars(x)
+  extra_info_meta <- paste(cli::col_yellow("metadata:"), meta)
 
-  cat(
-    paste(
-      "A grouped chronogram", "\n",
-      "Groups:       ", paste(groups, collapse = ", "), "\n",
-      "... now printing chronogram view ...", "\n"
+  extra_footer <- paste0(
+    pillar::style_subtle(paste0("# ", cli::col_yellow(cli::symbol$star), " ", (extra_info))),
+    "\n",
+    pillar::style_subtle(paste0("# ", cli::col_yellow(cli::symbol$star), " ", (extra_info_meta)))
     )
-  )
-
-  NextMethod(x, ...)
+  c(default_footer, extra_footer)
 }
+
+
+#' This is draft code to fine tune display of the pillars themselves.
+#'
+#' #' @importFrom pillar ctl_new_pillar
+#' #' @importFrom pillar new_pillar_component
+#' #' @importFrom pillar new_pillar
+#' #' @export
+#' ctl_new_pillar.cg_tbl <- function(controller, x, width, ..., title = NULL) {
+#'   out <- NextMethod()
+#'
+#'   pillar::new_pillar(list(
+#'     top_rule = pillar::new_pillar_component(list("========"), width = 8),
+#'     title = out$title,
+#'     type = out$type,
+#'     mid_rule = pillar::new_pillar_component(list("--------"), width = 8),
+#'     data = out$data,
+#'     bottom_rule = pillar::new_pillar_component(list("========"), width = 8)
+#'   ))
+#' }
+
diff --git a/R/print_chronogram_skeleton.R b/R/print_chronogram_skeleton.R
deleted file mode 100644
index bc866cb..0000000
--- a/R/print_chronogram_skeleton.R
+++ /dev/null
@@ -1,61 +0,0 @@
-#' print chronogram skeleton
-#'
-#' @param x a chronogram skeleton object (class cg_skl_tbl)
-#' @param ... additional arguments passed to tibble::print S3 generic
-#'
-#' @return print to console
-#'
-#' @export
-#' @examples
-#' \dontrun{
-#' small.study <- chronogram_skeleton(
-#'   ids = c(1, 2, 3),
-#'   start_date = "01012020",
-#'   end_date = "10102021"
-#' )
-#'
-#' ## print, with default tibble options ##
-#' small.study
-#'
-#' ## print, with eg 3 rows ##
-#' print(small.study, n = 3)
-#' }
-print.cg_skl_tbl <- function(
-    x, ...) {
-  calendar_date <- attributes(x)$col_calendar_date
-  ids_column_name <- attributes(x)$col_ids
-  version_number <- attributes(x)$cg_pkg_version
-
-  cat(
-    ## use paste to prevent cat re-formatting dates
-    paste(
-      "A chronogram skeleton:\n",
-      "Dates column: ", calendar_date, "\n",
-      "IDs column:   ", ids_column_name, "\n",
-      "Starts on:    ",
-      min(x %>% dplyr::pull(calendar_date)), "\n",
-      "Ends on:      ",
-      max(x %>% dplyr::pull(calendar_date)), "\n",
-      "Spanning:     ",
-      max(x %>%
-        dplyr::pull(calendar_date)) -
-        min(x %>% dplyr::pull(calendar_date)) + 1,
-      " days\n",
-      "Contains:     ",
-      x %>%
-        dplyr::pull(ids_column_name) %>%
-        factor(.) %>% nlevels(.),
-      " unique participant IDs\n",
-      "Size:         ",
-      rlang::parse_bytes(
-        as.character(
-          lobstr::obj_size(x)
-        )
-      ), "\n",
-      "Pkg_version:  ",
-      version_number, "[used to build this cg]\n\n"
-    )
-  )
-
-  NextMethod(x, ...)
-}
diff --git a/R/summary_chronogram.R b/R/summary_chronogram.R
new file mode 100644
index 0000000..8318f56
--- /dev/null
+++ b/R/summary_chronogram.R
@@ -0,0 +1,135 @@
+#' summary chronogram
+#'
+#' @param x a chronogram object (class tbl_chronogram)
+#'
+#' @return print to console
+#' @examples
+#' \dontrun{
+#' ## a 3-person chronogram_skeleton ##
+#' small_study <- chronogram_skeleton(
+#'   col_ids = elig_study_id,
+#'   ids = c(1, 2, 3),
+#'   start_date = "01012020",
+#'   end_date = "10102021",
+#'   col_calendar_date = calendar_date
+#' )
+#'
+#' ## Create a tibble containing some metadata for our 3 individuals ##
+#' small_study_metadata <- tibble::tribble(
+#'   ~elig_study_id, ~age, ~sex, ~dose_1, ~date_dose_1, ~dose_2, ~date_dose_2,
+#'   1, 40, "F", "AZD1222", "05/01/2021", "AZD1222", "05/02/2021",
+#'   2, 45, "F", "BNT162b2", "05/01/2021", "BNT162b2", "05/02/2021",
+#'   3, 35, "M", "BNT162b2", "10/01/2021", "BNT162b2", "10/03/2021"
+#' )
+#'
+#' ## Set appropriate metadata column classes ##
+#' library(dplyr)
+#' small_study_metadata <- small_study_metadata %>%
+#'   mutate(across(c(sex, dose_1, dose_2), ~ as.factor(.x)))
+#'
+#' small_study_metadata <- small_study_metadata %>%
+#'   mutate(across(contains("date"), ~ lubridate::dmy(.x)))
+#'
+#' ## Make a chronogram ##
+#' small_study_chronogram <- chronogram(
+#'   small_study,
+#'   small_study_metadata
+#' )
+#'
+#' ## print, with default tibble options ##
+#' small_study_chronogram
+#'
+#' ## print, with eg 3 rows ##
+#' print(small_study_chronogram, n = 3)
+#' }
+#' @export
+#' @noRd
+#'
+summary.cg_tbl <- function(object, ...) {
+  x <- object
+
+  calendar_date <- attributes(x)$col_calendar_date
+  ids_column_name <- attributes(x)$col_ids
+  version_number <- attributes(x)$cg_pkg_version
+  windowed <- attributes(x)$windowed
+  meta <- attributes(x)$cols_metadata
+
+  zz <- NULL # suppress no visible binding warning
+
+  over_min <- x %>%
+    dplyr::group_by(
+      dplyr::across(
+        dplyr::all_of(ids_column_name)
+      )
+    ) %>%
+    dplyr::summarise(zz = (dplyr::n())) %>%
+    dplyr::pull(zz) %>%
+    min(., na.rm = TRUE)
+
+  over_max <- x %>%
+    dplyr::group_by(
+      dplyr::across(
+        dplyr::all_of(ids_column_name)
+      )
+    ) %>%
+    dplyr::summarise(zz = (dplyr::n())) %>%
+    dplyr::pull(zz) %>%
+    max(., na.rm = TRUE)
+
+  cat(
+    ## use paste to prevent cat re-formating dates
+    paste(
+      "A chronogram:\n",
+      "Dates column: ", calendar_date, "\n",
+      "IDs column:   ", ids_column_name, "\n",
+      "Starts on:    ",
+      min(x %>% dplyr::pull(calendar_date)), "\n",
+      "Ends on:      ",
+      max(x %>% dplyr::pull(calendar_date)), "\n",
+      # "Spanning:     ",
+      # max(x %>% dplyr::pull( calendar_date )) -
+      #   min(x %>% dplyr::pull( calendar_date )),
+      # " days\n",
+      "Contains:     ",
+      x %>% dplyr::pull(ids_column_name) %>%
+        factor(.) %>% nlevels(.),
+      " unique participant IDs\n",
+      "Windowed:     ", windowed, "\n",
+      "Spanning:     ",
+      over_min,
+      "-",
+      over_max, "days [min-max per participant]\n",
+      "Metadata:     ",
+      paste(meta, collapse = ", "), "\n",
+      "Size:         ",
+      rlang::parse_bytes(
+        as.character(
+          lobstr::obj_size(x)
+        )
+      ), "\n",
+      "Pkg_version:  ",
+      version_number, "[used to build this cg]\n\n"
+    )
+  )
+}
+
+
+
+
+#' @export
+#' @noRd
+summary.grouped_cg_df <- function(object, ...) {
+
+  x <- object
+  groups <- dplyr::group_vars(x)
+
+  cat(
+    paste(
+      "A grouped chronogram", "\n",
+      "Groups:       ", paste(groups, collapse = ", "), "\n",
+      "... now summarising whole chronogram ...", "\n"
+    )
+  )
+
+  NextMethod(x, ...)
+}
diff --git a/R/validate_chronogram_skeleton.R b/R/validate_chronogram_skeleton.R
index c75db9e..3a3892f 100644
--- a/R/validate_chronogram_skeleton.R
+++ b/R/validate_chronogram_skeleton.R
@@ -1,13 +1,13 @@
 #' validate chronogram skeleton
 #'
-#' @param x a chronogram skeleton object (class cg_skl_tbl)
+#' @param x a chronogram skeleton object (class tbl_df, with attributes that record IDs and date columns)
 #'
-#' @return Errors, or TRUE if valid cg_skl_tbl
+#' @return Errors, or TRUE if valid chronogram skeleton
 #'
 validate_chronogram_skeleton <- function(x) {
   stopifnot(
     "Invalid cg_skeleton: Wrong class. Use 'chronogram_skeleton()'" =
-      inherits(x, "cg_skl_tbl") == TRUE
+      inherits(x, "tbl_df") == TRUE
   )
 
   stopifnot(
diff --git a/chronogram.Rproj b/chronogram.Rproj
new file mode 100644
index 0000000..21a4da0
--- /dev/null
+++ b/chronogram.Rproj
@@ -0,0 +1,17 @@
+Version: 1.0
+
+RestoreWorkspace: Default
+SaveWorkspace: Default
+AlwaysSaveHistory: Default
+
+EnableCodeIndexing: Yes
+UseSpacesForTab: Yes
+NumSpacesForTab: 2
+Encoding: UTF-8
+
+RnwWeave: Sweave
+LaTeX: pdfLaTeX
+
+BuildType: Package
+PackageUseDevtools: Yes
+PackageInstallArgs: --no-multiarch --with-keep.source
diff --git a/data/built_smallstudy.rda b/data/built_smallstudy.rda
index d71d678..26ad727 100644
Binary files a/data/built_smallstudy.rda and b/data/built_smallstudy.rda differ
diff --git a/data/pitch_chronogram.rda b/data/pitch_chronogram.rda
index 773efe9..89d1e8a 100644
Binary files a/data/pitch_chronogram.rda and b/data/pitch_chronogram.rda differ
diff --git a/inst/extdata/pitch-database-output.sqlite b/inst/extdata/pitch-database-output.sqlite
index 1208e4a..707e112 100644
Binary files a/inst/extdata/pitch-database-output.sqlite and b/inst/extdata/pitch-database-output.sqlite differ
diff --git a/man/new_chronogram.Rd b/man/new_chronogram.Rd
index 190daa6..7c8b64f 100644
--- a/man/new_chronogram.Rd
+++ b/man/new_chronogram.Rd
@@ -7,7 +7,7 @@
 new_chronogram(x, metadata_cols, ...)
 }
 \arguments{
-\item{x}{a tbl, a daughter of a join between a cg_skl_tbl and
+\item{x}{a tbl, a daughter of a join between a chronogram skeleton and
 one (or more) objects coerced to a tbl.}
 
 \item{metadata_cols}{the column names from the metadata tibble}
diff --git a/man/new_chronogram_skeleton.Rd b/man/new_chronogram_skeleton.Rd
index cd60e50..dcb10d0 100644
--- a/man/new_chronogram_skeleton.Rd
+++ b/man/new_chronogram_skeleton.Rd
@@ -15,7 +15,7 @@ rlang::enquo(an_unquoted_string)}
 \item{ids_col}{provided as rlang::enquo(an_unquoted_string)}
 }
 \value{
-x a tibble with class cg_skl_tbl
+x a tibble with attributes to identify \code{calendar_date_col} and \code{ids_col}.
 }
 \description{
 A low level constructor function. Use the helper
diff --git a/man/print.cg_skl_tbl.Rd b/man/print.cg_skl_tbl.Rd
deleted file mode 100644
index 72be5db..0000000
--- a/man/print.cg_skl_tbl.Rd
+++ /dev/null
@@ -1,34 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/print_chronogram_skeleton.R
-\name{print.cg_skl_tbl}
-\alias{print.cg_skl_tbl}
-\title{print chronogram skeleton}
-\usage{
-\method{print}{cg_skl_tbl}(x, ...)
-}
-\arguments{
-\item{x}{a chronogram skeleton object (class cg_skl_tbl)}
-
-\item{...}{additional arguments passed to tibble::print S3 generic}
-}
-\value{
-print to console
-}
-\description{
-print chronogram skeleton
-}
-\examples{
-\dontrun{
-small.study <- chronogram_skeleton(
-  ids = c(1, 2, 3),
-  start_date = "01012020",
-  end_date = "10102021"
-)
-
-## print, with default tibble options ##
-small.study
-
-## print, with eg 3 rows ##
-print(small.study, n = 3)
-}
-}
diff --git a/man/print.cg_tbl.Rd b/man/print.cg_tbl.Rd
deleted file mode 100644
index a576b9d..0000000
--- a/man/print.cg_tbl.Rd
+++ /dev/null
@@ -1,59 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/print_chronogram.R
-\name{print.cg_tbl}
-\alias{print.cg_tbl}
-\title{print chronogram}
-\usage{
-\method{print}{cg_tbl}(x, ...)
-}
-\arguments{
-\item{x}{a chronogram object (class tbl_chronogram)}
-
-\item{...}{additional arguments passed to tibble print S3 generic}
-}
-\value{
-print to console
-}
-\description{
-print chronogram
-}
-\examples{
-\dontrun{
-## a 3-person chronogram_skeleton ##
-small_study <- chronogram_skeleton(
-  col_ids = elig_study_id,
-  ids = c(1, 2, 3),
-  start_date = "01012020",
-  end_date = "10102021",
-  col_calendar_date = calendar_date
-)
-
-## Create a tibble containing some metadata for our 3 individuals ##
-small_study_metadata <- tibble::tribble(
-  ~elig_study_id, ~age, ~sex, ~dose_1, ~date_dose_1, ~dose_2, ~date_dose_2,
-  1, 40, "F", "AZD1222", "05/01/2021", "AZD1222", "05/02/2021",
-  2, 45, "F", "BNT162b2", "05/01/2021", "BNT162b2", "05/02/2021",
-  3, 35, "M", "BNT162b2", "10/01/2021", "BNT162b2", "10/03/2021"
-)
-
-## Set appropriate metadata column classes ##
-library(dplyr)
-small_study_metadata <- small_study_metadata \%>\%
-  mutate(across(c(sex, dose_1, dose_2), ~ as.factor(.x)))
-
-small_study_metadata <- small_study_metadata \%>\%
-  mutate(across(contains("date"), ~ lubridate::dmy(.x)))
-
-## Make a chronogram ##
-small_study_chronogram <- chronogram(
-  small_study,
-  small_study_metadata
-)
-
-## print, with default tibble options ##
-small_study_chronogram
-
-## print, with eg 3 rows ##
-print(small_study_chronogram, n = 3)
-}
-}
diff --git a/man/validate_chronogram_skeleton.Rd b/man/validate_chronogram_skeleton.Rd
index 843df83..dc22746 100644
--- a/man/validate_chronogram_skeleton.Rd
+++ b/man/validate_chronogram_skeleton.Rd
@@ -7,10 +7,10 @@
 validate_chronogram_skeleton(x)
 }
 \arguments{
-\item{x}{a chronogram skeleton object (class cg_skl_tbl)}
+\item{x}{a chronogram skeleton object (class tbl_df, with attributes that record IDs and date columns)}
 }
 \value{
-Errors, or TRUE if valid cg_skl_tbl
+Errors, or TRUE if valid chronogram skeleton
 }
 \description{
 validate chronogram skeleton
diff --git a/tests/testthat/test-chronogram_skeleton.R b/tests/testthat/test-chronogram_skeleton.R
index 1a3a216..91f27f2 100644
--- a/tests/testthat/test-chronogram_skeleton.R
+++ b/tests/testthat/test-chronogram_skeleton.R
@@ -11,7 +11,7 @@ small_study <- chronogram::chronogram_skeleton(
 test_that("chronogram_skeleton: correct class", {
   expect_s3_class(
     small_study,
-    "cg_skl_tbl"
+    "tbl_df"
   )
 })
 
@@ -79,3 +79,45 @@ test_that(
     )
   }
 )
+
+test_that(
+  "chronogram_skeleton: includes an ID column in attributes",
+  {
+    expect_false(
+      is.na(attributes(small_study)$col_ids) |
+        is.null(attributes(small_study)$col_ids)
+    )
+  }
+)
+
+test_that(
+  "chronogram_skeleton: includes an date column in attributes",
+  {
+    expect_false(
+      is.na(attributes(small_study)$col_calendar_date) |
+        is.null(attributes(small_study)$col_calendar_date)
+    )
+  }
+)
+
+
+test_that(
+  "chronogram_skeleton: date column in attributes is a column name",
+  {
+    expect_true(
+      attributes(small_study)$col_calendar_date %in% colnames(small_study)
+    )
+  }
+)
+
+test_that(
+  "chronogram_skeleton: ID column in attributes is a column name",
+  {
+    expect_true(
+      attributes(small_study)$col_ids %in% colnames(small_study)
+    )
+  }
+)
+
+
+
diff --git a/tests/testthat/test-new_chronogram.R b/tests/testthat/test-new_chronogram.R
index 9e3c9bd..63ef3f5 100644
--- a/tests/testthat/test-new_chronogram.R
+++ b/tests/testthat/test-new_chronogram.R
@@ -17,15 +17,12 @@ by_hand_cg <- dplyr::left_join(
 
 
 
-test_that("input is not of class cg_skl_tbl", {
-  expect_error(
-    ## provide an input object of wrong class ##
-    new_chronogram(
+test_that("input chronogram skeleton is class tbl_df", {
+  expect_s3_class(
       metadata,
-      metadata
-    ),
-    "provided object does not inherit cg_skl_tbl class"
-  )
+      c("tbl_df", "tbl", "data.frame"),
+      exact = T
+    )
 })
 
 test_that("input metadata_cols not a character vector", {