In a study to measure BP, two students Rakesh and Arif conduct a study on a dog. Rakesh measures BP using a mercury sphygmomanometer on the right femoral aery and Arif measures using a pressure transducer and pulse tracing on the left femoral aery. The mean aerial pressure for both Rakesh and Arif is the same i.e.100 mmHg. After 5 minutes of injection of adrenaline, Rakesh measures blood pressure 130 mmHg and Arif as 120 mmHg. The difference of 10 mmHg is explained by: