Technician A is right, If we take standard atmospheric pressure as reference then pressure below atmospheric pressure is known as "vacuum" and is usually measured in inches of mercury Hg. On the other hand, the pressure above the atmospheric pressure is simply called "pressure".
Technician B is wrong, The MAP sensor compares manifold vacuum to a perfect vacuum to determine the pressure.The manifold absolute pressure (MAP) sensor is used in the electronic control system of an internal combustion engine.
