Travel along my Y axis is increasingly off with more travel. It is not detectable in the 100 mm span given for calibration, but at what g-sender says is 17", travel is about 17-3/8. Worse at 24 and 29. I’m stumped. Help or link to solution?
@Ump98 What machine are you running?
What controller are you using?
Does it do this at all jogging speeds?
Has it always done this, or is this a new issue?
LongMill Mk2 48x30 out of the box with g-sender. As I said, pretty new here. I believe this has been an issue from day one, but since I was just playing and was using larger stock, the position of the cut wasn’t critical. I noticed it was off, but I assumed I wasn’t setting zero correctly, somehow. I have been as careful and thorough as I understand, with the same problem now clearly evident. I just checked it at normal and rapid jog. The X is spot on, but travel on the Y is off the same amount at both speeds. It thinks it has travelled 17" (in this case) when it has traveled around 17-5/8". The calibration mode using 100 mm jogs is within a millimeter, and tells me I don’t need to update anything (but still gives the option). I am seeing at least a dozen reasons this could happen, and it may not be an easy solve. I really appreciate any thoughts you might have. You can’t much underestimate the green on me here. Thanks.
@Ump98 As often as not, these things are caused by things being too tight. If you have the new, spring-loaded anti-backlash nuts, back off the mounting bolts a bit, run the Mill fully backwards and forwards a few times, then snug them back up. The key word here is “snug”. Tighten just so the split washers on the mounting bolts are flattened and no more. If you have the older black ab nuts, first back off the adjusting screw all the way, then do the same with the mounting bolts.
Make sure the v-wheels are not too tight. For giggles, you can back the off so that they are definitely too loose and see if the calibration improves. If it does not, no loss. If it does you will know that you started with them too tight.
All this said, don’t lose heart or patience. Many here - me included - have been where you are . We lived. 
Thanks. Thats one of the several things I identified. It’s a place to go next. Not discouraged at all. I find this all very interesting. I knew from research I would need patience and persistence. Thanks again.
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Backed if the M5 bolts and checked the spring tension. It was surprusingly loose. Machine runs beautifully, but still can’t measure Y travel. Im going to try updating G-sender and flashing the firmware. Kind of a chore in my situstion but worth a try.
@Ump98 If you haven’t already opened a support ticket, you should.
Thanks. I will do that after trying a couple more things. Day job keeps me busy so it takes a bit for me to get things done.