I calibrated the tape speed all of 4 my Yamaha decks this past Saturday. The ceramic tipped screw drivers arrived, I had my tape, and multimeter with frequency measuring capability. The multimeter was an absolute bust ....i could not use it. I ended up using an Android app called Advanced Spectrum Abalyzer Pro by Vuche labs and the on board mic of the tablet. I chose to calibrate the KX800 first, the one with the recent belt replacement. Turns out, it playing the 3KHz tape at 3KHz so that machine was good. I then calibrated the KX1200 which was off by a 100Hz. It played too fast. This backed up my original findings via the ear and I know now that the KX1200 played fast. This means I have to rerecord between 12 to 20 cassettes. I calibrated the other KX800 which was just slightly faster, and the K700 which was also quite fast.