foxmouth - which seminar? I went to an ETA one and the method was commended to the audience who agreed with it. Shame it was explained so poorly. I've also seen notes from another seminar giving an incorrect and fundamentally flawed explanation...
The double-the-error-for-the-same-time 'method' assumes that a constant error has been flown and that you can afford to stay off track for the same amount of time as you have already been off track. It's old-fashioned and inadequate.
SCA+MDR=KISS........