Note ā as of BMS 4.36, this tool may now be redundant.
I notice the new [shift+3] āSA Barā overlay window shows the throttle position (and afterburner detent), on the indicator bar (mis-)labelled āRPMā.
For actual engine RPM, you can add it to the HUD with the following cfg:
set g_bNoRPMOnHud 0
Also new to 4.36, you can have an audible click when passing through the AB detent:
set g_bAfterburnerDetentClick 1