Equipment:
– Ardupilot APM1.0 (1280) + Oilpan
– MB 1240 XL-EZ4 Sonar from Maxbotix
– Frame Gaui 500X with 330X-S  Motor/Speed

Result:
After adjust some ALT_HOLD_P and THR_P gain. Overall Altitude hold was good. Because of beam behavior on EZ4. It may cause altitude change immediately a bit.

And some test on barometer hold was ok. I believed my Oilpan board is too old and not in a 100% condition. Sone circuit and sensor may not good.