I have a Tower Hobbies Digital Mini tach and I guess it works alright. Seems though I can't get a steady reading on it. I have a Saito 72 so maybe it's the engine, but say for instance, at idle it will show between 2,200 to 2,600 or higher rpm and it really jumps around. Same on the high end. And when I angle it up or down a little the reading is totally different. Is this just how these tachs are or am I doing something worng. I hold it behind the prop about 3 or 4 inches.

Make sure that when you tach the motor, the sun is at your back. Sunlight, shop light, etc.... can mess up the readings.

Thanks, the sun was at about my 1 o'clock position. I'll have to try that.

Hold it a little closer to the prop, Closer....Closer....Brararararararararart...ok, back up a little....THERE. Just kidding, about a foot or so is plenty close; proximity will also help minimize the jumpy reading, as will jtemple's suggestion.

Try it with a flashlight pointed through. That will prove if its a lighting issue. If that still produces jumpy readings, then you may have a tach problem.

Duke

Sorry to borrow this thread but I have a small tach question and there's no need to start a new thread:

The instructions for my Hobbico tach says to try it towards a fluo lamp and the reading should be 3600 for two blade and 2400 for threeblade prop.
My tach reads 3000 and 2000, do we have another hz here in Europe that messes up the American manual suggested reading?
I've tried it on all kinds of lamps, and get consistent readings of 3000/2000

Your reading is correct, we have 230V/50Hz in most western european countries while the americans are stuck with 110V/60Hz. 3600 * 50 / 60 = 3000

Thanks Norway!

if you have a CRT monitor, you can check your tach with that also, just hold it close to a solid white screen, and check what your monitor refresh rate is on... (you can usually go down to 60 hz, which should be 3600, 75 hz should be 4500 rpm.)

I find it works well if I am in the shade to point towards a brighter area. In other words if the prop is backlit as long as the glare of the sun isn't hitting the lens of the tach.