Should ones arm be resting on surface or hold itself ( elevated without support) at heart level while checking blood pressure?

Resting always: When you hold your arm up, you're performing muscular work /isometric exercise: this raises your BP! Your arm must be supported at heart level on a table or desk to obtain an accurate reading. (also: be sure you're at complete rest for 10 minutes and that the cuff is the right size for your arm's diameter). Thank you for asking - that's a great question!