Register columns resizing

[Leslie Katz]

I am definitely the king of silly questions!

Suddenly, at least some of the columns in my registers are of different 
size than they used to be. Some are now so narrow that the start of 
multi-digit numbers in them can no longer be seen. It's very irritating.

I tried putting the cursor over the lines dividing the headings of the 
columns and then dragging the lines, but they seem to return to their 
existing positions as soon as I release the mouse button.

Is there some combination of keys I should be holding down while I try 
to drag the dividing lines?

Alternatively, is there some other mechanism for resizing register 
columns? I looked for one, but didn't find it.