diff --git a/ch08.adoc b/ch08.adoc
index e11e0bdb..5c47903a 100644
--- a/ch08.adoc
+++ b/ch08.adoc
@@ -409,7 +409,9 @@ assumed to be zero.
 The **`interpolation_parameters`** attribute may only be provided if
 allowed by the definition of the interpolation method. Interpolation
 parameters may always be provided to non-standardized interpolation
-methods.
+methods. 
+
+The interpolation parameters are not permitted to contain absolute coordinate information, such as additional tie points, but may contain relative coordinate information, for example an offset with respect to a tie point or with respect to a combination of tie points. This is to ensure that interpolation methods are equally applicable to both coordinate and bounds interpolation. 
 
 The interpolation parameter variable dimensions must include, for all of the interpolated dimensions, either the associated subsampled dimension or the associated interpolation subarea dimension. Additionally, any subset of zero or more of the non-interpolated dimensions of the tie point coordinate variable are permitted as interpolation parameter variable dimensions.