Small and large holes

The spacing between the center of the perfs remains approximately the same (there is a very slight difference, but only measurable beyond 2cm, so you won't notice it on the stamp nor when measuring with a basic perforation gauge). The primary difference is that the holes are smaller, so the teeth appear slightly fatter. You need a speciality gauge to really measure it -- although if you collect them in pairs you should see the difference pretty quickly. The gauge is helpful if you have a single stamp and no reference stamp to directly compare. Here is a snippet from my Precision US Specialty Multi Gauge (revision 4):



Notice that with the small holes, technically the perforations per 2cm is actually a tad bit smaller than the normal large hole perf 10 variety.  But you don't really notice it until you get into the 2-3cm range.  The pic above is for illustration purposes, you would need to scale it properly in order to print and use (that is why I included the mm ruler).  It is better to get the physical gauge, although I do use the digitized version to check stamps I have already scanned.