Electronic weighing equipment greatly simplified the mechanics of weighing large, heavy aircraft. Figure 3-15 shows one type of electronic scales. The complete weighing kit is contained in a portable carrier. Included in the kit are a steel tape, plumb bobs, spirit level, straightedge, hydrometer (for determining the fuel specific gravity) and the load cells. The load cells are actually strain gauges that reflect the load imposed upon them by the aircraft in terms of voltage change. This change is indicated on a scale that is calibrated to read in pounds.

One load cell is placed between the jack pad and the jack at each weighing point. Each load cell must be balanced or "zeroed" before applying any load to the cell. After completing the weighing operation, remove all load from the cells and check to see if the cell reading is still zero. Any deviation from zero is referred to as the "zero scale shift" and constitutes the tare when using electronic weighing scales. The direction of shift  

is the factor that determines whether the tare is added to or subtracted from the scale reading. Always follow the instructions of the manufacture whose scales you are using.