How critical is the exact placement of the tonearm

Hello All,
There is a minefield of information on this thread for newbies. It does explain however, that when I put a different type of allignment tool on my Rega P3 many years ago, I couldn't get the geomtry right.

Anyhow, that arc protractor sounds helpful. Does anyone have a link for that Gent in Hong Kong who makes one for under $100?

Also, where does that old Mobile Fidelity alignment disc (the one that was the size and shape of an LP) fit into all this? Is the Mobile Fidelity disc Baerwald geometry? Is that disc an accurate enough tool to use in the correct alignment of arm and cartridge?

Hi Swampwalker- thanks for the link. Looking at the info on their site- the customer sends their tonearm and turntable brands (and also cartridge?) and they make a tractor specifically for that set-up?