Built a couple of DistoXes for the West Sussex Caving Club over New Year. The conversion is quite fiddly but simple enough. The main difficulty was removing the screws from the Disto. The case is held shut by a torx (6 pointed star shaped hole in the screw head) size 12 screw with a centre pin, and the internal screws you have to remove require a torx size 7 (which we could not find for love nor money). We had a torx size 12 bit with the hole to remove the screws with a pin, but having stripped the edges off a torx size 6 bit attempting to remove the screws, I realised the bit was tapered, and removed the end with a hacksaw to create a 6+ sized bit which did the job.
The conversion requires 4 wires to be soldered onto pads on the DistoX board, and then onto the Disto original circuit board. The pads on the Disto original board are in the middle of the board, and only about 1mm x 1mm, so experience of soldering fine electronics, good eyes and steady hands are required.
Job done on both units, and I have borrowed one to play with. Calibration is simple but slightly time consuming. The good thing is you do not need to take any reference readings to calibrate the unit. You just need to record 56 shots (in groups of 4, rotating the Disto along the long axis by 90 degrees between each one (i.e. The first horizonal leg is taken with the screen up, then screen to the left, then screen towards the floor, then screen to the right). As long as you keep the device on station and the laser on target for each of the 4 shots in each group, the actual directions do not matter. The device then automatically uploads the 56 readings to the PDA. One button press executes the calibration process and an error factor is displayed. If it is 0.5 or less you have done it right, and just select from the PDA menu to upload the data back to the DistoX. So this can be done in a cave or out in the field if you need to change the batteries and want to recalibrate.
Testing it today the readings matched my Suunto Tandem compass/clino as closely as it is possible to read the Suunto. Can't wait to try it out underground now!