diff --git a/doc/bc.1 b/doc/bc.1
index eeda08b..7ff6a2d 100644
--- a/doc/bc.1
+++ b/doc/bc.1
@@ -175,6 +175,8 @@ The result of the expression is the sum of the two expressions.
 The result of the expression is the difference of the two expressions.
 .IP "expr * expr"
 The result of the expression is the product of the two expressions.
+If a and b are the scales of the two expressions, then the scale of the result is:
+min(a+b,max(scale,a,b))
 .IP "expr / expr"
 The result of the expression is the quotient of the two expressions.
 The scale of the result is the value of the variable \fBscale\fR.
diff --git a/doc/bc.texi b/doc/bc.texi
index 40034ab..0bc9c80 100644
--- a/doc/bc.texi
+++ b/doc/bc.texi
@@ -291,6 +291,8 @@ The result of the expression is the difference of the two expressions.
 
 @item expr * expr
 The result of the expression is the product of the two expressions.
+If a and b are the scales of the two expressions, then the scale of the result is:
+min(a+b,max(@var{scale},a,b))
 
 @item expr / expr
 The result of the expression is the quotient of the two expressions.