Dunno. I had someone working on it, and the ground was harder to detect reliably. Depends a lot on exactly how you are doing the equivalent of virtual ground. Just for fun, we tried making the lame a capacitor by having two conductive layers and an insulator between them. That improved reliability considerably. You can make a fastener-less tip that incorporates a strain gauge. You do have to calibrate. Yes, you do it with the weight. I'd probably make the weight have RFID or equivalent, so you know which weight is being used, and so you could pull up it's actual weight and make the calibration more accurate.