You can do the sensor calibration before or after you calibrate the ESCs. Same difference. But you do have to plug the battery with the radio bound to the quad and with the throttle stick at 100% to calibrate the ECS. Apparently, you can plu the battery and THEN immediately press/hold the two buttons to invoke ESC calibration. But I always just hold the buttons while I connect the battery. The V1 version of the KK2 firmware doesn't allow you to plug the battery and press the buttons next, so I got used to do it that way, even though, I don't think it's necessary with the v1.2 firmware.
The KK2s I ship are all flashed with the 1.2 firmware, and by the way, they are new so they have the protective film on the LCD. Also, 2 out of 3 of these boards come with a loose LCD panel. It's a quality control issue that has been reported by most people. I do fix that before shipping them, too.
Off to my shop. I just finished flashing 32 ESCs and 8 KK2s
Have a nice weekend, gents.