AHA Guide for Blood Pressure (heart.org):

A difference of greater than 10 mm Hg between right and left arm signifies an increased risk of cardiovascular disease.
ACE Guidelines for Body Composition

Please note: In general, bioelectrical impedance (for example, using a handheld device) is relatively precise but not extremely accurate.
The Omron-500 series scale (using hands and feet) has been shown to be fairly precise and accurate.
Don’t dwell on your body fat percentage. Accuracy can be affected by food in your gut, hydration levels, lotion, sweat, or monthly cycles. It’s more important to pay attention to relative changes over months and years as these reliably indicate changes in body composition and reduction of risk factors for disease.
ACE Waist-to-Hip Ratio

Demonstration:

