I have both but the Technics protractor in the library is IMO superior in operation as you can set the overhand perfectly using the curved line rather than having to find it by trial and error as with the HFN.
When I originally set up the cart I used the Technics Arc protractor. In the list of protractors here there is also the Thorens Arc protractor v.2, my spindle to pivot distance appears to be just over 215MM, could it essentially be 215.6 or are these considered the same in regards to the two protractors? I know in calculating anything that .6MM is alot so this is why I ask.
I measured my effective length and it looks to be right at 234.5MM. I have a different printer now so I cannot go back and check the previous protractor but this one is printing slightly large...about .5-.7MM large on both the straight test rulers.