Old Make Do Ruler with Hand-Carved Numbers - Presumed for Liquid Measure

Best understood through detail photos, this ruler measures 12 inches long, but is carved with numbers that do not correspond to inches, but rather I believe marked liquid ounces. What I really like about this--in addition to the smooth, beautifully worn wood that makes it just a pleasure to hold--is that clearly it was a particular solution to a particular situation, I would think  made to use in conjunction with a very specific vessel, perhaps a milking bucket? And it seems that the 2-3 oz range was important, and then again 10-13 oz, but no need to worry about anything in between! I just can't resist make do sorts of tools like this--tender, perfectly imperfect things.

12" l x 1 1/8" w and in very good condition.