2. You can Click directly on a bookmark. This will erase that number.
To Get it back if you change your mind you will have to use the right click method.
3. If there is only one bookmark left you can click on it and that number will be set as the blocks number.
4. If there is only one left you can also double click anywhere on the block and the Number will be set.
NB. Remember that if the warning check button is checked as the default you will receive a warning an any error that you make and the change will not be done.
You can highlight a number to assist you in seeing patterns on the board. (only one at a time)
You can also highlight naked doubles and select none to clear highlighting.