The "844" is the S.C.O.R. approved digital in car Voltage meter used to move the teching of batteries on race day along with ease.  These hand calibrated voltage meters are with in .01 +/- of the 8.44 voltage allowed for most dirt oval applications.  These voltage meters are great for tracks who want the racers to self police their voltage or to help move tech along and keep the lines shorter.  Each voltage meter is hand calibrated and sealed with a tamper proof decal and backing screws are filled in.  The are constructed of a lightweight 3D printed case and digital voltage readout.  They come with 6+" of wire that can be soldered directly to the ESC.  Each case comes with 2 3mm mounting holes or can be double sided taped down to a flat surface.  This is a great tool for each track that runs any sort of stock/spec racing.