What you are need to read is the resistance of the pinion within the backlash. That is ,with the wheel on the ground, turn the flange. It turns a little. What you are measuring is how hard the pinion turns within the slop of the ring gear.
You can reuse the nut (if you don't destroy it) this way the nut should be in the same spot when you have the torque set right.
You will need a inch/lb dial torque guage. You measure the torque before you remove the nut. Then add several (don't remember the amount of inch/lbs) when you put the nut on and tighten it down.
You need a ft/bls torque guage to measure how much you torque the nut too. If you go over the spec. lbs while trying to get the correct resistance between the backsash, you will need to replace the crush sleeve, BIG JOB.
If you are lucky, you will just tighten the nut to where it was when you removed it.