CAD tip # 6678:

If you need to insert blocks with incrementing numbers in attributes, or automatically renumber existing blocks in your DWG drawing, you can use the free CADstudio InsertC utility. InsertC contains two commands - InsertC and BlockC.

The InsertC command is a "counting" version of the INSERT command. It inserts a specified block and automatically fills its first (resp. specified) attribute with an increasing number in a series. You can either specify the block by picking an existing reference, or by entering its name.

The BlockC command takes the selection set of existing blocks and fills (renumbers) their first (resp. specified) attributes with a series of incrementing numbers. You can sort the blocks (influence the numbering order) by their selection order, or by their X- or Y- coordinates.

Both autonumbering commands allow to specify the starting value of the counter, the prefix and the postfix for the generated number. You can also use the insertc:Inc LISP variable to set the increment (if other than +1), insertc:Prec for decimal precision (for decimal increments) and insertc:AttNo to specify the attribute number.