Why don't we use the whole vial of regent for testing in the Mastertronic?

Why don't we use the whole vial of regent for testing in the Mastertronic?

This question is asked a-lot, that we get a refill warning for the regent when we get to 7mil in the vial and you ant bypass it?

The reason is very practical!  

  • We have a stir bar in the vial for keeping the heavy/thick regents suspended 
    and if we let the needle go down past the 7mil, the needle could hit the bar and bend.