Hi there James, I have been using a similar concept for a while now using a piece of 7/16 key steel measured off the cross slide and is much more accurate than the old eyeometer
.
It looks like we have the same lathe, AL-320G, if so, it is a reasonable machine.
I have recently had to replace the output shaft and key as it became loose and was starting to leave chatter marks on my finishing work.
cheers
Graham