Whether to say anything

What do you say, if anything, when a health care worker performs a procedure and you're pretty sure it's not done correctly.

Example: Lately when I have had a manual blood pressure taken at my provider's office I have noticed that certain personnel seem uncertain of the results they obtain and their results vary quite a bit from my usual range. Of course, blood pressure does vary, but it's more the vibe I get that the person doing this did not really hear the markers and guessed at some numbers. I have been told before that my blood pressure is hard to hear. I don't want to insult anyone or even make anyone feel bad, but I do want an accurate reading. What should I say? Or should I just keep my mouth shut?