Why does my mom get different readings.first time its 140 then comes to 120 in a gap of few seconds.she takes it in digital machines.

Need to wait.: If someone repeatedly checks their blood pressure on the same arm two and three times successively, one would see that the numbers go down. This is not accurate, though, but more reflective of the repeated effect of the BP cuff on the vasculature. One must wait ten minutes before checking the BP again on the same arm. For quick repetition, check on the opposite arm.