Accidental magnifier!
I was looking at JetBlast, as one might, when I mistimed - and misfingered - some clicks on my mouse and there appeared a circle superimposed on one of the postings. Within the circle, the text was highly magnified. Moving the mouse moved the circle over the text - magnifying whatever fell below the circle. Once I had tired of this, I tried to get back to my normal arrow cursor by clicking the mouse buttons but to no avail. One button varied the magnification within the circle while the other cycled between differently-sized circles and squares and even rectangles!
The problem is that this seems a very useful function but I still don't know which inadvertent combination of clicks got me there (or out again!) so I haven't been able to repeat the exercise!
Is there anywhere that I can find information about this and, perhaps, other hidden functions?