I think it’s more fun this way.
---
doc/groff.texi.in | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/doc/groff.texi.in b/doc/groff.texi.in
index dda99b83a..56fdce530 100644
--- a/doc/groff.texi.in
+++ b/doc/groff.texi.in
@@ -6015,7 +6015,8 @@ Inch; defined as 2.54@tie{}centimeters.
@cindex @code{c} scaling unit
@cindex unit, scaling, @code{c}
@cindex scaling unit @code{c}
-Centimeter; a centimeter is about 0.3937@tie{}inches.
+Centimeter; the distance light travels in vacuum when given the
+2,997,924.58th part of a second. That is about 0.3937@tie{}inches.
@item p
@cindex point scaling unit (@code{p})
--
2.44.0
