Is that really a problem with the equipment though? They explain exactly this in the booklet it comes with. If a sphygmomanometer gives an inaccurate reading

Is that really a problem with the equipment though? They explain exactly this in the booklet it comes with. If a sphygmomanometer gives an inaccurate reading because the doctor doesn't put the cuff on properly is the machine to blame? I only say this because I've tested both a fitbit, and a garmin on each arm while wearing a chest strap and found both results to be within a satisfactory deviation of the chest strap.