Your build surface is calibrated before it leaves the Type A Machines Factory to print the initial layer of an object at an even height. The build surface calibration bolts feature two finger nuts. A bolt passes through the build platform, with one nut above and one below. These nuts work together to adjust the height of the Build Plate and then to lock the adjustment in.
If you are experiencing problems with first layer adhesion when a portion of the first layer is properly adhered and another portion is not, first replace the blue tape on the print surface and try again. If problems persist you MAY need to re-calibrate your build plate.
To adjust one corner of the build surface higher, gently loosen the lower nut and tighten the upper nut of the corner that needs adjusting, then tighten the lower nut to lock the adjustment in.
Caution: make sure your hot end is cool. Clear the build surface of any prints or other materials. Launch Pronterface and move the build platform down. Place the included 7mm wrench on the build plate in the front right corner. Use the open head of the wrench as a milled standoff block. (see photo below on left)
In Pronterface, move the tool head to be directly over the wrench. Move the Platform so it is almost touching the wrench (see photo below in middle)
Now adjust the two finger nuts until the wrench comes in light contact with the Extruder Nozzle. You should be able to move the wrench around under the head while feeling light resistance from the contact. (see photo below on right)
Remember to tighten the lower nut to lock the adjustment in. Manually move the tool head each of the four corners, place the wrench beneath the Extruder Nozzle and repeat knurled nut adjustment procedure. You build plate should now be Calibrated. Confirm this by moving the wrench and head to the front right. You may need to tweak this bolt since you have adjusted the others, and you may need to adjust the height of the first layer using the Z-endstop trigger.