hello all:

Well just couldn't help hopping in here, great topic.

Well from my perspective, and experience for what it may be worth, here is what I used for many years and hundreds of mortices later. My preference and what I used for quick and accurate work, and for rough hewn surfaced timber was a 2" shipwright's auger for a 2" mortice, driven by a heavy duty 1\2" electric drill (be careful). I levelled the timber using the markout lines on the end, and then using a short torpedo level along 2 of the sides of the auger started the inward travel of the bit.
I then stopped, and checked for level once again and then finished to the depth. I had a short 1" by 2" stick placed on the top of the timber, and under the case of the drill to stop the inward travel. The length of this stick was pre determined for that particular mortice, For mortices that went right through, I drilled half way from the two opposing sides, this always seemed to work well, in my books nothing works better than a shipwrights auger for accuracy. this proceedure needs help from a journeyman or helper.
NH