How can opticians be so wrong?

Question

Hi there. I've had contact lenses for a few years now. Recently, I've went to a few opticians to try different brands of lenses and each optician has given me a different prescription.

Opticians 1:

L= -1.00 -1.25 x 160

R= -1.25

Opticians 2:

L= -1.25 x 160

R= -0.75

Opticians 3:

L= -0.25 x -1.25 x 160

R= -0.50

As you can see, there is no doubt that I've got -1.25 of astigmatism in my left eye on axis 160, but how can those 3 readings vary so much. I don't know which to trust. Can anyone see any logic behind this?

Answer 1

#1 was off quite a bit but 2 and 3 are almost the same

Answer 2

It really looks like just the first one was off.  The next two are actually very similar.