Ovulation positive then negative?!?

[Dezzyh99]

I took 2 ovulation tests of the same brand.
Yesterday the Clearblue advance digital ovulation test came back with flashing smileys (high)
I took 1 today from a new package with a new reader and it said blank circle (low) took another one of the same kind that I had from the other pack since they are reusable and it had a flashing smiley (high)...
What could cause this. It started being high on the first and has been since. I'm confused..

 

[ama]

Your LH surge is average only 24hours i believe. Some are shorter some are a little longer . Hopefully you got to bding with the first positive . x