There are 4 sizes of the Stehende (Standing) Helvetia stamp. When I'm identifying them, I start with vertical perforations as a means to quickly narrow down which series they are from. In the Zumstein guide (they refer to the perforations as zahne or teeth).
11 3/4 x 11 3/4 - 14 teeth
9 1/2 - 9 1/4 - 11 teeth
11 1/2 x 11 - 13 teeth
11 1/2 x 12 - 14 teeth
If it's not clear when looking at an image which of the two versions with 14 teeth I see and I really have to know, I'll copy the image, and then copy just the teeth portion from the side and paste it back on the image but rotate it to see if the teeth line up. If they due it's 11 3/4. If they don't it's 11 1/2 x 12.
The post date is an immediate give away on this, as the the beginning of the run of Stehende Helvetia's was 1882 and they were 14 zahne versions. They did not issue 14 zahne versions again until 1901.
For a more in-depth discussion of Stehende Helvetia's, you might look at this thread I started here where I was trying to get information about watermarks -
https://goscf.com/t/81495 .
It's definitely easier to identify those with a postmark than mint versions and the paper type and watermarks add complexity for sure. There are 67 main versions of the stamp in the Zumstein catalog with 6 of them being very rare. I have a spreadsheet that helps me quickly filter by teeth, value, paper and watermark. It definitely helps narrow things down quickly.
BTW this would be Zum - 72A, Mich - 63XA, and Scott 87.