eratic timing

[charger Downunder]

I bought a new advance timing light and it shows eratic timing on my 440 with orange box ignition, i can still use it to set the timing it jumps now and then.
When i put my  inductive timing light on all is well no problems perfect timing exactly at 12 before no movement at all.
Has anybody experienced this with these advance timing lights.

[Nacho-RT74]

 

myself... still wondering why... dunno if some electrical or mechanical deal.

I'm not the only one, a friend of mine with a Dart too. I'm with chromed box, my friend with stock box. the erratic "reading is around +/-1 or 2 degrees

[charger Downunder]

Its the advance timing light i asked the old bloke at the local auto store and he said he has had numerous complaints with them. He said to use it and then check with with standard light.