Tormek makes a very nice small square. You get one "for free" if you purchare the Anniversary Black T8. Unfortunately, this small square is not yet available as a stand alone accessory. HOWEVER, there is a relatively inexpensive "plan B". Although the TTS-100 is primarily designed for setting woodturning tools, it can also work very well with vhisels and plane irons. It makes a very fast, accurate setting tool and a useful small. Wolfgang demonstrates this at 1:07:20 in this video:
https://www.youtube.com/live/7aHmc43RUY4?si=av0B0hGR-tWmKWQy
Wolfgang demonstrates this with a skew chisel; however, many things in sharpening cross function.
Ken
PS The first time I sharpened a turning skew, I did not know the TTS-100/ small square trick. I assumed my skew angle matched the Tormek diagram. This "sharpening" turned into a lengthy reshaping project. A wiser plan would have been to draw the square line and set the skew angle to just a little closer to the recommended angle. After several sharpenings, I would have gradually matched the angle. A markedcollar with the third setting left blank initally would have tipped me off.