I think DFC is right. The lowest DA for an IMC pilot is 500' + PEC and the lowest MDA is 600. I admit to having to rummage through my notes and the Thom book for confirmation. I was taught to add 200' to the OCH and use the greater of 500'/600' and the OCH+200 and then add the PEC for a precision approach. If I recall my conversations with the CFI correctly, the adding 200' bit is recommended. the 500'/600' is a must.