Although I'm sure some people will disagree, I don't advise using the camshaft as an accurate point to base ignition timing on.

It is fine to be used as an RPM pick up (which is how the std ERST works) but the only accurate way to control an ECU for igntion timing is from the crankshaft.

This is because the cam timing relative to the crankshaft will drift at high rpm due to belt lift. This invariably means that an ignition system that bases its reference position on the camshaft will drift from the setting at idle with rpm.