I have a wristech modelzsbp-002.Half way...

I'm not really sure what error i had with this type of blood monitor but i found that the problem was with the two little knobs behind, that were stick out too much . If you put your finger behind the blood monitor , in the area that comes in contact with the wrist, you should feel two little knobs under the textile material. If they stick out too much try to gently push them in. Hope this is work....

With wrist BP monitors errors frequently occur because the senors in the cuff are not positioned correctly. The manual should indicate the corresct placement of the cuff. Arrows on the cuff also help with correct placement. The arm/wrist shoud be kept still while the machine is measuring and the arm/wrist should remain in a flat level surface with the elbow bent at a 90 deg angle and not hanging down. Over the counter auto BP machines are reliable when the instruction of correct placement of the cuff are followed.
Hope this helps.