diff --git a/hledger/hledger.m4.md b/hledger/hledger.m4.md
index ab019198c..232ae9588 100644
--- a/hledger/hledger.m4.md
+++ b/hledger/hledger.m4.md
@@ -4056,6 +4056,16 @@ amount %amt %cur
 Note we used a temporary field name (`cur`) that is not `currency` -
 that would trigger the prepending effect, which we don't want here.
 
+### Amount decimal places
+
+Like amounts in a journal file,
+the amounts generated by CSV rules like `amount1` influence 
+[commodity display styles](#commodity-display-styles), such as
+the number of decimal places displayed in reports.
+
+The original amounts as written in the CSV file do not affect display
+style (because we don't yet reliably know their commodity).
+
 ### Referencing other fields
 
 In field assignments, you can interpolate only CSV fields, not hledger