As long as the color continues to change, you continue counting drops. There are two things to watch out for. If you are not swirling enough you might have missed the color change changing more on an earlier drop, so slow down a little right near the end. Second, if the changes are really really small it could be an illusion or visual error, so don't worry about little tiny almost invisible color changes.
So TA 140, and CH somewhere around 160, 170 or 180.
So TA 140, and CH somewhere around 160, 170 or 180.