For a Mk1 or 2 telescope, don't even bother wasting your money with the 'correct' tool (which one is correct.....) They were all a complete waste of rations. Just leave the lead screw locking nut (the outer nut with forked recesses) nipped up so that the inner lead screw (the reverse headed one) can be turned with a little bit of friction. Now you can simply zero using a suitably sized allen key with a slot cut across the end on the brass lead screw. Then zero it like that......, carefully, carefully a bit at a time and it'll stay put for ever.
Only buy the 'tool' if you want it to look good and to impress your friends in the telescope box - but NEVER use it. And NEVER lock up the lead screw locking nut up over finger tight and NEVER be tempted to use a pair of pliers either.