mechanical usualy use a vacum line to get their reading, which is sometimes not always correct
electrical just splice into an electrical line & are more accurate 'cuz they use electricity, instead of a mechanical device, such as a vacum line.
That's sort of the right answer. Yes mechanical gauges use a vacuum line of some sort for their readings. But most electrical gauges (depending on what it is your "gauging") also use a vacuum line. The vacuum line just runs to an electrical sender which in turn runs to the gauge instead of just a vacuum line to a gauge. The reason most people would rather use electrical gauges for most things is that it keeps a vacuum line out of the interior of your car. Say you've got an oil pressure gauge; most people would rather have the vacuum line full out hot oil stay in there engine bay and just run to an electrical sender rather than mess around with a line full of hot oil running inside their car.