Update ch08.adoc

Co-authored-by: David Hassell <davidhassell@users.noreply.github.com>

ch08.adoc

@@ -695,7 +695,7 @@ Use of these conventions ensures that all quantized variables are clearly marked
 
 These conventions must not be used with data variables of integer type, or any other kind of CF variable.
 This is because fields that describe idealized or reference coordinate grids, or grid transformations, are often known to the highest precision possible.
-These fields can include spatial and temporal coordinate variables (e.g., **`latitude`**, **`longitude`**, **`level`**, **`time`**) and properties derived from these coordinates (e.g., **`area`**, **`volume`**).
+These variables can include spatial and temporal coordinate variables (e.g., **`latitude`**, **`longitude`**, **`level`**, **`time`**), properties derived from these coordinates (e.g., **`area`**, **`volume`**), and variables referenced by the **`formula_terms`** attribute of a coordinate variable.
 Degrading the precision of such grid properties may have unintended side effects on the accuracy of subsequent operations such regridding, interpolation, and conservation checks which should generally be performed with the highest precision possible.
 For the same reason, it is recommended not to quantize any data variable which is referenced by a **`formula_terms`** attribute of any variable.