Recently brought a trial lens set off eBay. On first test it seems I was wearing weaker glasses then required so I switch to a older pair yesterday, that resulted in a bit of a head ache by the end of the day, something very rare for me.
So today, I been testing using the lens kit and discovered something is indeed off but not the glasses(!) as after a while I worked out the diopter given in the lens set is 0.25 more then various corresponding glasses. So for example -3.25 lens match a -3.0 glasses. -3.0 lens match my 2.75 glasses etc.
Quite shocked about quality of the lens set especially as one of the points of a having a trial lens set was getting more accuracy in my diopter readings.