No, what I said was you leave the 'check cable' with known weight in place, 50# is not going to stretch 3/16 9X9 cable. THEN, when you are ready to check tensions, you take the tensiometer TO the suspended 'check cable' and using the correct block, you check to see if the tensiometer reads within acceptable parameters so you know that what it reads on the in airplane cable is set to the correct tension. When done, put the tensiometer back in it's box so it won't fall onto the floor until you're ready to check the next cable. One calibration check a day should be OK for the entire day. Boeing has 'check cables' in numerous locations in the assembly bays in every factory each one has a routine inspection routine tag attached which is on a tooling inspection schedule and the weight is prominently noted on the attached tag with a steel stamp, and as an Inspector, part of your job when doing tension checks is to check the tensiometer.
Don't EVER leave a tensiometer attached and closed on a cable as it will screw up the tensiometers calibration as you've noted. As with any calibrated tool or device, if it's dropped send it out for a cal check before using it again and put it on a say yearly rotation for re-cal, it's cheap insurance.
That make s alot more sense after some more sleep!
