Roger,

You don't have to have a tach. If you follow the guide lines like you have so far, then you'll be OK. Concentrate on other things for now.

Yes you most likely will need to adjust at least the high speed needle if you change props. But most people can adjust the needles by the sound of the engine.

Some people have bad hearing and need a tach if they cannot feel the plane and tell what the engine is doing?

Now, if you need some snob appeal to keep your syche going, then by all means get one. Then you can come back on here with certain bragging rights about how many rpm's your engine turned.

A tach is nice if your really intrested in engines and you want to try to get the last bit of power from one. But you don't have to have one.

I've never seen anyone get their tach out at the flying field. A lot of the fellows probably have them but I suspect the only person I'll ever see at the field with one will be some new guy.

I have a TNC tach which is expensive and no longer made, but it stays in the shop. I don't take it to the field.

Good luck,

Jim