here is a batavus service manual.
the laura m48 and m56 engines are adjusted the same way. at 2mm btdc the points should break. you can test this with an ohm meter or test light.
if you go to this link;
i explain how to make a piston depth guage to measure 2mm piston drop btdc so that you can adjust the points on a batavus. i cant remember the wire colors, but in the service manual it tells you which wire you can hook an ohm meter to so that when the engine turns you can see whether or not the points break.