how did you figure to calibrate?
In another thread, Michael described the process.
Here I'm paraphrasing:
1) with all 4 build table screws loosened, tell the printer to adjust to build level by typing command “g”
2) adjust the build table to be flush with vat by putting light pressure downward, then tighten all 4 screws.
3) focus the projector on the build table by looking from the bottom and adjusting the two focus rings.
4)undo the main thumb screw to remove the build table. (so we don't ruin the vat coating when we remove it)
5) reset the printer, which moves the build table to to 57mm or so.
6) carefully remove the build table from the vat surface and reattach it by thumb screw.