Various embodiments of a semi-automatic sphygmomanometer apparatus that automatically determines whether a vascular cuff is configured with a large volume or a small volume are disclosed. The semi-automatic sphygmomanometer apparatus includes a pump in fluid flow communication with the vascular cuff and a processor in operative communication with a pressure detector for detecting a first plurality of cuff pressures over a first plurality of times and a second plurality of cuff pressure over a second plurality of times. At any stage during the inflation cycle including partially inflated vascular cuffs prior to re-inflation of the vascular cuff, the processor calculates a first average cuff pressure based on the first plurality of cuff pressures and a second average cuff pressure based on the second plurality of cuff pressures and then subtracting the first average cuff pressure from the second average cuff pressure to determine a slope value which is compared against a boundary value to determine whether the vascular cuff is configured with a large volume or a small volume.
