If you want to check tension or set tension on an Esprit with the round belt tooth (HTD profile) like your 89.
Then this is the method that you should use.
cell phone frequency tensioning for me!
I use the app called "Speedy Spectrum" on my Android phone. Works great for finding the first fundamental frequency of the belt.
https://docs.google.com/open?id=0B2...YjEyLTgyZTAtYmI5NjE4MjgxMmRm&authkey=CO_S1NoE
Engine is cold and at 30deg before top dead center (30 BTDC).
Microphone is placed close to the belt, as close as possible. Reach around the front of the engine and strum the belt in the middle between the intake cam pulley and the oil pump pulley. Strum it like a guitar string, do not let the finger touch the belt after the strum, slip the thumb off quickly with one motion.
This is for cars with the round tooth HTD belts only.
Standard software settings, though make sure to turn on peak hold and enable peak hold overlay. you can zoom in on the screen near 100Hz, but I look at the peak hold number in the upper right of the screen.
30 BTDC
Note CAM dots are slightly mis-aligned and not centered on the axis at 30BTDC
Speedy Spectrum at 103Hz on my HTC EVO 3D Android phone
Thumb technique