Ok, so I've been using my monitor for 4 cycles now. With it and BBT I have pinpointed OV on CD 16. Last month, when we had our first offical TTC the monitor suddenly skipped from low to peak on CD 11 when previously it would always slowly progress and usually start moving from low to medium on CD 12 or 13 with peak days following. A real disappointment when we are carefully trying for a cut off for a girl and really wanted accuracy on when the LH starts. BBT later proved I still OVed on CD 16 as usual and the monitor was wrong. Has this happened to anyone else? I had been using silk and had a ph around 4.4 - can silk or low ph affect the monitor? Could the presence of DH sperm do this either? I just hope this does not happen on our next attempt! I don't understand what might have gone wrong last cycle!