> Measurements at different points in time can differ slightly... Indeed! The best thing you can do before an eye exam is be rested, eat an apple, don't stare

> Measurements at different points in time can differ slightly... Indeed! The best thing you can do before an eye exam is be rested, eat an apple, don't stare at your phone in the waiting room, look out the window if there is one. Tired eyes will give differing results. Low (or high) blood sugar (even in healthy people) with give differing results. Straining your eyes by looking at a screen in the waiting area can give differing results. Note for all these I say can and not do.