RPM's - Rotax Tach vx GRT EIS Tach

This owner with the 200 rpm difference just reads the correct rpm and doesn't bother with the wrong one.

i am surprised nobody has noted how to check this.  Get a prop tack, see what the spinning blades tell you.  For a geared engine like Rotax to get crank speed multiply that by the gearbox ratio for crank.  

You can buy GA aircraft type units or even use simple RC tack/prop testers.  

Cheers

Second try - This Post was completely removed after being accepted.

RW,

If you check back I think you will find that your advice pretty much duplicates mine;

To independently assess engine RPM, I used;

A cheap copy of a "Tiny Tach"  induction tacho. Also useful when tuning chain saws.

A DynaVibe dynamic propeller balancer. Borrowed, then purchased for future prop balance/checks.

A cheap laser RPM meter. Used in tuning small motors eg mowers.

I compared all three readings with my Dynon SkyView EFB (EMS) and adjusted the EMS tacho to reflect the combined information.

I suggested that Tim do something similar.

😈

Sean, agree with you.  There are a lot of good options and it should be done at initial build and test run of the aircraft to verify your instruments.  Since RPM is so critical for prop settings as well as making sure you do not go beyond limits.  

Cheers mate

“A DynaVibe dynamic propeller balancer. Borrowed, then purchased for future prop balance/checks”. 

Ok Sean, the gig is up. You’re really not against buying expensive, occasionally used, tools! Just like the aircraft scales sitting on my shelf.  😬