[PATCH] doc/groff.texi.in: Define the centimeter.

[Lennart Jablonka]

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