If you're noticing that the RPM readings are consistently double the expected RPM, it's likely because the hardware division settings haven't been adjusted in the software. For example, if you're using a 3-blade propeller, the RPM division should be set to 3 to account for the extra blade. Failure to do this will cause the system to register a false pulse.
To adjust the division settings, Go to the Hardware tab. Under the hardware device, select the Built-in System tab. Scroll down and click the settings icon next to Rotation Speed. A message box will appear, allowing you to select the appropriate divider amount.
Making this adjustment should correct the RPM readings.