The luggage scale I use for calibration is on the cheap end, but I trust (and have tested) it to be good to the nearest pound.
Whenever I test my Wise, it pulls right to the programmed in reference tension and holds there, exactly like I want it to. If I connect the scale to the tension head with a soft poly that relaxes under tension (e.g. ISOSPEED Baseline), the Wise will continue pulling as it relaxes to keep the tension right.
There's some minor fluctuation as the string relaxes and the tension head pulls a tiny bit further to bring it back into the ideal range, but it's always close on the scale and appears to match the readout on the Wise.
USRSA MRT - Wilson Baiardo
Pro Staff 97 - Natural Gut/Black Magic