Trying to setup gasser and a Saito low end using a tach.
Have used three different brand hobby tachs(hobbico, Hanger 9, Globe). Can not get consistent good readings outside in sun light to properly set up my low end needle. Have plane facing sun or direction of sunlight shooting thru prop from back within 4 to 6 inches. Readings are way off or not consistent. Calibrated fine, batteries good. Can not set up my low end with out consistent readings. What am I doing wrong?
HELP

Learn to hear when the engine sounds smooth - the tach is just good for recording -NOT setting
anyway - to read props -- use white fingernail polish and paint last inch of backside of prop white -
avoid really direct sunlight - but stand behind prop and move tach back and forth and at angles to the prop till you find the sweet spot - it really may be back a foot - reading will be very constant and repeatable.
The least expensive little tachs such as the Hanger 9 -read as accurately as the most expensive ones you can find.
The reason is the same as why a 10 dollar watch is as good as a 10,000 dollar one -for accurate (accurate enough) time
Current electronics have made this type of instrumentation dirt cheap and accurate.

ditto what Dick said - the human ear is one of the best tuning tools you can get, if you have a good ear. I hate hearing a 2 stroke twin that one engine is about 2 clicks leaner than the other, I mention it to the other guys around me, and none of them can hear the dissonance. I go and tweak the engines for the guy and then everyone says - ahh sounds better now.

I found that it is best to not have the plane pointed where you are aiming your tach into the sun. Also - make sure if you are under your carport, or in an enclosed shop, that you don't have any overhead incandescents or flourecents turned on. I've had issues at times with the carport lights throwing my tach reading off.

The instructions in my Hobbico tach stated if your readings are fluctuating, then you need to turn the model 90 degrees - never had to try it, but it's something to remember.

My hearing is shoot after career in Infantry. To properly tune low end on a Zen G-26 the experts give a technique of using tack but must get consistent readings to work. Not what the exact RPM is but when it tops out. Same with setting a stubborn Saito 100 on low end for war bird.
I was on the thought process of getting direct in sun. On painting prop will relook that or even try to use white chalk as temp measure. Doing my tuning at field.
Thanks for input

Get the TNC tach. They are sold by Fromeco now.

Point the nose of the plane at the sun. Point the tach from behind the prop at the sun.

Dick has a good point and now after some experience with both glow and gas engines, I can hear when things are a bit out of whack, but I like to confirm things when setting up and then go by ear while flying to make sure things are okay. But if you are new, or can't really hear the differences for one reason or another, then a tach will definitely help.

BUT rajul is right... [8D]

When I first tried the tach thing I got one of those GloBees (sp?) and although it seemed to work pretty well, I did have problems with it depending on ambient light. So I got one of the TNC tachs and after comparing the use of the two in different light situations, different color props and differences in tach readings, I gave the GloBee away...