Ignition timing, Ignition timing confusion Options

[aeginc77]

Help! I have never timed my 914 before. I changed the points to electronic ignition and have got a very fast idle. I am prepared with my timing light to check the timing but am confused. I see the v on the impeller shroud and have located the white dot on the impeller ( I assume when both of these are lined up #1 piston is at TDC). I also have a template thanks to Pelican Parts to mark 27degrees before TDC. Do I mark 27 degrees on the shroud where the v is or mark the impeller? I would assume I would see the white dot on the impeller at 27 degree mark marked on the shroud when the timing light flashes. Or do I mark the impeller at 27 degrees BTDC and see the flash at the v on the shroud? I thought I had this until I saw a picture on Pelican Parts of an impeller with a 27 degree mark on the impeller.