Absolutely. NEVER EVER do anything in the front or the sides of a running motor. Props can and do break or come off. You don't want to be in the path of one that gets thrown. Always stay away behind a running motor. See attached diagram.

First thing on the tach is to test it to make sure it is working properly. Turn it on to the two blade setting and point it at a fluorescent light, it should read 3,600 RPM. The reading may differ, but the reading should be a multiple of 60 (this is because your electricity runs at 60 hertz and a fluorescent light actually "flashes" on and off with the electricity. And yes, other countries run their electrical current at 50 hertz). If the tach is working properly then you should do as stated above. Take the reading from behind the prop, and try to have the sun on the other side of the prop.

Hope this helps

Ken