This is a non-invasive measurement of the strength of the urinary stream. You should arrive with a full bladder and will be asked to void into a machine that measures the amount of urine voided as well as the flow rate. It is usually followed by an ultrasound measurement of post void residual, to see how much urine is left remaining in the bladder. Takes approximately 30 seconds to complete but expect to be at the appointment from 15-20 minutes. You should arrive with a full bladder. There are no after effects.