In reply to red1200:
A good tip for anyone not yet converted to the EDK.
Leave long tails, 18 inches to 2 feet. Its good practice to have a back up in the systen, if the abb tat is say around a tree, use a long sling around the tree and clip it to the abb rope, leave enough slack so that it'll come into force should the tat snap. The heaviest climber should abb first while the lighter one will remain in place watching the setup for any problems. Once down and clear of the rope, the heavier climber will test pull the ropes a few metres to make sure they'll clear the tat/edge of cliff etc. Now the lighter climber can abb knowing that the whole set up took a heavier climber without problems so he can remove the back up before abbing.
Now, those tails you left - everything in the system is as safe as you can make it yet the main knot that allows the abb to happen is not tested or backed up. This isn't a problem if the knot is tied correctly but climbers new to the EDK may have that niggling doubt in the back of their minds. Simply clip a screwgate to the backup sling and tie off the 2 tails with a clove hitch to this additional crab. If you think the knot will start to roll, you'll know the tails are tied off and will stop the roll before reaching the ends. One the heavy guy is down, remove the tail tie offs as they are no longer needed and leave the rope clear for the heavy guy's test pull. The heavy guy's job is not yet done, he needs to hold the bottom of the rope ready to pull tight and stop your abb should their be problems. He can stop you dead should he wish simply by pulling from the bottom end. This isn't a replacement for your prussik but again, yet another safety trick.
Belt and braces it may well be but something i do all the time and I do abb a fair bit. You see folk setting up their abbs and they quite correctly, they use all the safety systems we know about. Prussiks, backed up anchors, proper knot with tails etc yet just a few secs to tie off the tails will give you that bit of reassurance.
Not wishing to sound patronising but rather just giving noob's some confidence while trying something new but dangerous.