i keep on getting dizzy but i don't have an arm blood pressure monitor, is there a way to measure your blood pressure without one?

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I'm with my grandmother right now, and she needs her blood pressure taken. She has a Target model Blood pressure monitor, manual inflation. I've done it before, and I think I'm doing everything right, but could somebody tell me how to do it? She can't tell me because she's too drowsy. It has a screen reading, but I do have to pump it myself, and deflate it. thank you very much in advance!!