I think arc template is really good, of course it is always more accurate a lasered Mint Protractor is the most accurate. I have many tonearms the Mint Protractor only works with one tonearm because it is only made for the spindle and the selected tonearm.that's expensive for me for 6 tonearms.Dear @DasguteOhr I see that you’re using a diy arc protractor and I think arc protractors are better than the others.
the problem with diy arc protractor is printing. I used the same program you use and even drawn some protractors using autocad. I tried several printers in professional printing shops from various brands. it is almost impossible to get precise printing of the pdf file. I printed out the same protractor and measured it in 1/20mm precision maybe 50 times and ended up piles of unusable protractors. after a lot of unsuccessful attempts I found out that only a professional printer (big ones almost 5mt. long) should be used with same paper all the time and with right printing scale (0.9981). maybe that number work for you too. you should also find a way to precisely measure 200mm lines and pivot to spindle distance on protractor in order to be sure the scale is right. IMHO measuring precision should be 1/20mm or better.
another problem is cutting the spindle hole. since it should be exactly 7.18mm in diameter and there isn’t a hole punch at that diameter the only option is using 7mm punch. precisely centering punch while cutting the spindle hole is very important and is very difficult.
I spent a lot of time to overcome those problems but if I knew that in the beginning I would simply buy a generic arc protractor like wallytractor.
IMO if you have sme 309 and up, use sme’s own paper protractor. and for the rest use a laser etched arc protractor preferably wallytractor. whatever you use the most important thing is precisely setting the arm/cartridge in line with protractor’s. using iphone’s magnifier really helps.
Of course, you have to measure the print result with a precise ruler.
therefor is 100mm and 200mm marking to see if everything fits
here is a little video of how it handles the spindle hole. I am satisfied I can adjust each tonearm and try out different zero points.