1.)This system uses a light source below a standard level vial and photosensitive plates above it. When the shadow falls equally on both plates, the bubble must be centered and therefore level. If the reading is lopsided, the device has electronic indicators to show which way the tool needs to move in order to achieve level. 2.)This bubble vial has three wires embedded in the glass: one in the center near the bottom and one on each end. A tiny current flows through the liquid from the center wire to each end and the electronics monitor the impedance at each end. For both ends to read the same, there must be equal amounts of fluid on each side of the bubble. 3.)This vertical, segmented disc has four sections and is constantly monitoring the current flow between them. Only two can be immersed in the fluid at the same time, and they must be covered equally by the fluid to read the same. Once the device is installed and calibrated in a laser like Zircon's LVX, it will read both level and plumb, depending on which two segments are active.