Need help reading RPMs on Geo Tracker

[sina27]

Hey everyone
I have a 1992 geo tracker 8 valve TBI, 5 speed 4WD. 
Im retuning the motor: 
Calibrated TPS, adjusting air bleed, and doing dynamic timing. 

From what I understand the motor needs to be hot and at 800rpm. How do I confirm 800rpm? The dash rpm gauge isnt too accurate-
When the motor is fully warmed up I can adjust idle using the air bleed screw until it seems like its 800rpm (clockwise makes it lower rpm), but I rather use an accurate digital gauge to determine the actual RPM.

what kind of device do I need to determine that actual RPM, and how would I go about doing this ( where would i connect it to)

Thanks

[fixkick]

any automotive RPM meter works or timing lights prime grade have rpm meter in it as bonus (uses spark wire =#1 as mag input)
https://www.amazon.com/INNOVA-3568-Digit...ive&sr=1-4

or any optical RPM meter with reflective tape on crank pulley rim . I point it the gun at tape mark and super accurate.
but why do it>?
but the dash gauge is ok, if the hot engine holds very near 800 and REGULATES, that is true 800. (+=50rpm)
to prove ISC is working and ecu and prove, regulation turn on headlamps and dash blower to full at same time. and RPM must hold 800, 1second wiggle is ok but 800 happens.
if not the ISC is not working for lots of reasons. (ecu inputs wrong is why) if ISC mech, not stuck in gunk mess)

connection RPM classic meter is to COIL minus pin and is not easy to do , that, as it is MOLEX type connector and hard to get to that pin. yes.
set meter to 4cyl and 4 cycle engine. mode.

first make sure all is good in my other post first.
then timing is last.
keep in mind idle and timing are related, if timing is retarded much RPM falls and means not ISC goes nuts. then you recalibrate ISC and get 800 then set timing freeze
and then RPM goes way higher, due to correct timing and burning more fuel not wasted, and not ISC is out of calibration again.
yes a pain ,until 1999 and fixed CKP sensor and distributor is gone. or J18 engine happened.1996.
yes.
once timing is correct it stays so and all else now is easy to fix and set, and calibrate for sure ISC, duty cycle seetings,
ISC is best set with $5 dirt cheap, analog DC voltmeter with needle meter. (seen even at walmart)_
set bleed so ISC has 7vdc at idle, meter across the 2 ISC pins ,as this gets you to 50% duty cycle on ISC easy
in DC volts the meter needle averages the ISC pluses. and is cheap duty meter, used like this.
200 HZ square wave it is and 1/2 high and 1/2 low 0v is 50% the above is the trick.
cheers,
ask for more can do.