The DPO3000/MSO3000 Aux In is equipped with a TekVPI connector to provide power for TekVPI accessories or TekProbe BNC accessories using the TPA-BNC that can be terminated into 1MOhm. However, because the Aux input has an input impedance of 1 MOhm, the instrument will display an "incompatible probe" message when a TekVPI active probe such as the TAP1500 is connected. The error message can be cleared and the probe can still be used. But TekVPI probes such as the TAP1500 and TekProbe probes such as the P6245 (used with the TPA-BNC) are expecting to be terminated into 50 Ohms, and therefore the signal delivered to the oscilloscope will be twice the expected amplitude, so the trigger level will have to be set at twice the expected value.