How To Measure Stamp Design?

I think Clark's suggestion about measuring [US] stamps was great advice - "A ruler is useless for measuring stamps". Best and fastest is to compare against an unambiguous reference stamp.

I can see where a ruler would be useless, since most aren't graduated finely enough. But I have been going through some 2cent2's (scott A140), and keep running into ones that are larger in BOTH dimensions than a flat plate impression of the same design.

One in particular is a 2c Washington, perf 10 vertically, unwatermarked, which is likely rotary press, but it measures 19.6 x 22.5 mm!

Should I just chalk this up to paper shrinkage of the flat plate version in both dimensions, and less-to-no shrinkage of the coil stamp in either direction?

Check the type of the stamp. Most rotary press stamps were type II or type III. Most rotary press stamps can be spotted because appearance and colors differ from type I flat plate stamps. Differences are significant enough to allow experienced dealers and collectors to identify without a magnifier. Of course, initial identifications should be confirmed by taking a careful look at details that differ by die type. Early type I rotary press printings on watermarked paper display brighter colors than later type II and type III rotary press printings.

Flat plate stamp are different enough from rotary press stamps that most can be identified without magnification. But, collectors wishing to become proficient must put in the necessary time and look carefully at a lot of stamps.