What is a tell-tale pointer on a pressure gauge?
A tell-tale pointer on a pressure gauge is a red pointer attached behind the black needle. Other names this is commonly known as is a tattle-tale pointer or drag pointer. It records the maximum pressure the gauge has experienced.
As the pressure increases the black needle moves up the pressure gauge, bringing the red needle along with it. The red needle does not move easily, therefore as the pressure decreases, the black needle returns to zero and the red needle stays in place. This allows the user to determine the maximum pressure that was reached by the gauge. The red needle can then be reset using the key in the centre.