Replace the mercury in the reservoir to the zero mark. Use a syringe and needle to draw up the mercury from the plastic bottle. Keep the needle under the surface of the mercury to avoid returning any black powder. Replace the reservoir top with its sealing ring, connect the cuff and check the system is airtight by inflating the cuff until the mercury is at the top of the column. Check that it does not spill out-if this happens, the top leather disc is faulty or missing.
Mercury continues to rise slowly after stopping inflation .
This is caused by the air at the top of the column failing to escape through the top leather disc quickly enough as the mercury rises up the column. When the sphygmomanometer is used, this fault may result in abnormally high readings as the mercury falls more slowly than the cuff pressure, due to the faulty leather disc restricting the air entering the top of the column. The cause of these faults is in the top leather disc. It is either too thick or dirty. It should be removed as described before and cleaned.