Meaning of a potentional tolerance value for a dimension in a mechanical drawing
Number of holes

2-Ø2.30 means two holes, each 2.3mm in diameter.  It would be more usual to write this as 2xØ2.30, but given the numbers match the number of holes drawn, I'm confident it's correct.

There are several different formats for dimensional tolerances, but all the ones I know of are either 1) two separate numbers, usually one above the other, 2) placed after the dimension or 3) follow the strict rules of GD&amp;T