Hitchcocks Forum

I have a 1936 S2 to which I have fitted a Thorspark ignition system. I have timed the ignition at 1/8" BTDC using a rod through the plug hole, however aligning the rotor on the Thorspark is a bit hit and miss, so want to use my timing light and disc. Can anyone confirm for me how many degrees on the timing disc equates to 1/8" ?

Thanks in advance.