Sit or lay down quietly for 5-10mins
Take heart rate and blood pressure readings
Stand up and keep as still as possible - No flexing calf muscles or weight shifting as these actions help to push blood around and compensate for any autonomic dysfunction
Take heart and blood pressure readings every minute for at least 10 minutes unless you get enough info earlier.
It is normal for the heart rate to rise by up to 25 beats. If it rises by 30 or more, and/or reaches 120 it meets the criteria for POTS.
It is normal for blood pressure to rise slightly or stay the same when you stand. If it drops (I'm not sure of the criteria for how much) it is considered orthostatic hypotension which would give you a diagnosis of OI (orthostatic intolerance).
Further investigation would be needed to determine whether it would be NMH (neurally mediated hypotension) or whether it was another form of OI
Also note symptoms - nausea, lightheadedness, dizziness, sweating, pallor, feeling awful...
Be sure to have someone with you as this test can result in a faint even if you don't normally faint. We don't usually force ourselves to stand still if we have "issues" with standing still!