The Ludlum Model 35 is a versatile, lightweight, vehicle-mounted instrument with an external detector used for alpha, beta, or gamma radiation survey. It remains unobtrusive until an alarm level is reached. When an alarm level is reached the monitor can be quickly removed from the mount for closer inspection. Three modes of operation – RATE, MAX, and COUNT – are available for the user. Measurements can be collected in two sets of units (primary and secondary) for RATE and MAX modes in cps, cpm, Bq, dpm, R/hr, rem, or Sv/h units. The user can switch between two sets of chosen units by simply pressing the Units button.