Zero elevation is a condition in which zero value of the measured variable is more than the lower range value.
The example of zero elevation is in DP transmitter c/w diaphragm seal and capillary tube installed above the lower process tap in measuring atmospheric tank level, one port is connected to process while the other port is exposed to the atmosphere.
In this condition, the fluid in capillary gives negative pressure on the transmitter which cause the the DP transmitter provides negative pressure reading at lower range value.