I have more than 40 years of bikes mechanics behind me and I have never had a torque wrench !
You can only go to the physics of the thing : a torque T is the product of a force F and length for moment arm
if F is perpendicular to the arm .
I use a little thingy for checking the luggage weight than you can find in any shop in airport . Its range is from 0 to 40 kg
I made a notch on my cliquet wrench at 25 cm from rotation point and , if when I pull the thingy to 36 kg ( for exemple)
with an angle of 90° with the wrench , i know that I have a torque of 36/4 = 9 kg.m !
And the thingy is arount 10 to 15 euros !
And you can use this for calibrating your expensive torque wrench