1. The main switch of the mercury tank is not turned on.
2. Mercury column can be displayed, but it drops too fast to be maintained. It is estimated that it is related to the air tightness of the whole sphygmomanometer, and there may be air leakage.
3. Good air tightness. Turn on the switch, there is no mercury column. Considering that the mercury tank or pipeline is damaged, the watermark has leaked.
In view of the toxicity of mercury, if you suspect that there is something wrong with the sphygmomanometer, you should send it to a special medical device maintenance point or find a seller to return to the factory for maintenance. If you buy it for a long time, you can buy a new sphygmomanometer to avoid inaccurate measurement.