You will need to run the autocalibration before your print job and without resetting your printer as the calibration values will be erased after reset if I am correct.

It is always best ot have the printer running optimal without autocalibration, as the adjustments will propagate up into your object. Let us say that one corner of your object has a zposition of -0.5 mm and you autocalibratte for this. Then the top part of your object will also be 0.5mm lower if the firmware does not even out things in the first couple of mm of printing.

The kinematics of a delta printer depend very strongly on the dimensions of the rods (0.1 mm difference unaccounted for in the firmware calculations makes a LOT of error in positioning), the relative positions of the three towers, and the degree in which the three towers are parallel (not skewed/leaning).

You can find a very good read up (including the effect of very small errors on the positioning) here: http://www.reprap.org/wiki/File:Rost...nematics_3.pdf

If you want to get a minimal error of say 0.1 mm over the full build plate, you will most likely need to make adjustments in the firmware as to individual rod lengths and tower positioning. A writeup of what you need to do and where you can change the Marlin firmware to accomodate differing rod lengths and tower positions are here: http://www.thingiverse.com/thing:745523 You will need to change the Marlin firmware source code, compile it and upload it to your printer.

The problem is that your printer needs to be reasonably printing to get your calibration object done in the first place. That is where the software optimization program I mentioned before comes in handy. If you can accurately measure the tower positions at those 7 points, the software will tell you which combination of rod length and tower positions gives you the most flat printing plane. With that as starting point, you can then print the calibration object and work onwards from there.

Again, if you provide me with the numbers I can run them through the software for you.