After employing the various techniques and being happy with my $4 manometer I bought one of these: http://www.advrider.com/forums/showthread.php?t=701625
It was the tach feature that sold me (early GS = no tach).
That and the portability, convenient size & etc.
I'm loving it: removes the fiddly business and BANG, yer done.
Mike & Spencer should be by shortly. I have a NIB oil pressure switch collecting dust on a shelf here, going to put it in service.