Can be used very successfully by the skip to cross check brushers' backline to hogline estimate. In general, stop watch timing can be used by the skip and brushers. Since I throw with two hands, I can test backline to hogline or hogline to hogline myself with a stop watch. I don't use this method in a game since it might be considered unfair. I am not aware of any competitive rule barring the practice however.
Some skips seem to always ask for a shot into new pebble.
The skip and brushers MUST remember where the rocks traveled in the last end and also remember if that path was brushed. This method means you count out in seconds and tenth's of seconds. Contrary to what a level 4 CCA coach told me, you can count out from the hack. This same coach, prior Brier curler, dares not curl against me for money. In the city, curlers in competitions regularly play at many clubs and get more practice in learning to read different ice conditions.