7 mistakes that can cause high readings when blood pressure is measured. 1, Holding your urine may cause a high blood pressure reading of 10 to 15 mmHg, so you should urinate before taking your blood pressure. 2. Sitting in the wrong position can also cause high readings. When taking a blood pressure reading, place your back against the back of a chair and your feet flat on the floor or on a footstool. 3, arm overhang may cause readings about 10 mmHg high, the arm should be placed flat on the table, so that the height of the cuff and the heart level and then measured. 4. A cuff placed over clothing may cause the reading to be 5 to 50 mmHg higher than it actually is. When measuring blood pressure, it is best to bare the arm. 5. A cuff that is too small or too tight will cause errors, so choose a cuff that is the right size. 6. Sitting cross-legged or stilting your legs while measuring blood pressure will result in a higher reading. 7. It is recommended to remain silent when taking blood pressure measurements to avoid unreliable readings.