Automatic or manual ringing. 4 measurement ranges from 40 to 130 db. 0.1 db resolution. option of fast or slow response times. a quality product from mastercool, usa.
Measures 5 important hvac parameters - temperature (f or c), humiditysound level (db), light level (lux), air velocity (fpm) and air volume (cfm)data holdone hand operationinstrument tripod & carrying case includedcfm chart included.