Setup ESPRIT 100 ED + AS178 MM + EVOGUIDE + ASI 178 MM @OHP Objective is to check if change of RA & DEC belts changed the PEC for the better, in particular removing the 10 s frequency. Replaced the RA belt with a 72 teeth one instead of 71 PHD test very good after cairation 0.6" rms Atofocus 12330 PEC Sans PHD, with PEC curve loaded. But periodic error present ??? Why ???? Remeasure PEC PEC2 Really strange, no periodic error at 480 s !!!! Did check that PEC correction was off M27 Some eposres ofr Hervé PEC3 re-measre again ... Not a long enogh easurement bt want to try correcting main period not there. 3 firt hamronics PEC4 Correctino loos O on a half period