A digital video recorder is described. The system may identify vehicles and individuals entering or exiting the zone through image recognition of the vehicle or individual as compared to prerecorded information stored in a database. One aspect of the invention is a retrofit of a conventional Geiger-M\xfceller meter to include a microcontroller with internal AD converter enabling the meter to output instantaneous measurements in RS-232 serial format. In assembly, the sliders are attached to opposite sides of a storage device. The back-end AGC function modifies its gain to unity if the front-end AGC function selected the luma signal peak amplitude for modifying its gain.