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This post was authored by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

### A plant has a 30-foot-high water tank mounted on top of a 70-foot platform. What is the water level in the tank, measured in feet, if a pressure gauge on the first floor, height 5 ft, reads 40 psi?

a) 22.3
b) 27.3
c) 30
d) 10
e) none of the above

40 psi translates to 92.3 feet of water, which won’t work in a 30-foot-high water tank and isn’t one of the answer choices. This means that the 40 psi measurement did not transmit down to that five-foot level, but that there is an actual physical device and system stretching that distance from the bottom of the water tank to that point five off the ground, below the platform.

There’s 92.3 feet of water, subtract the 70 feet of platform height, add the five feet above the floor where the meter measurement happens and one ends up with 27.3 feet.