Then using the protractor, I found the cartridge was very square to the grid pattern, without having to slightly twist the cartridge one way or the other using the alignment protractor only

Easy to use... just square your cartridge up in the head shell and you're good to go.

An absolute necessity for aligning a new cartridge...and works perfectly with my Audio-Technica LP120.

and if you're good enough at squaring the cartridge in the headshell, there's no need for a protractor.

Works as it should and is a direct replacement for the one included with Technics SL-1200 type turntables.