CA Health & Safety Code Section 114157

(a)

A thermometer shall be provided for each refrigeration unit.

(b)

The thermometer shall be located to indicate the air temperature in the warmest part of the unit and, except for vending machines, shall be affixed to be readily visible.

(c)

Except as specified in subdivision (d), cold or hot holding equipment used for potentially hazardous food shall be designed to include and shall be equipped with at least one integral or permanently affixed temperature measuring device that is located to allow easy viewing of the device’s temperature display. Alternative hot or cold holding equipment can be equipped with approved product mimicking sensors placed in devices located in the warmest part of the mechanically refrigerated unit in lieu of an ambient air sensor.

(d)

Subdivision (c) shall not apply to equipment for which the placement of a temperature measuring device is not a practical means for measuring the ambient air surrounding the food because of the design, type, and use of the equipment, such as calrod units, heat lamps, cold plates, bainmaries, steam tables, insulated food transport containers, and salad bars.

(e)

Temperature measuring devices shall be easily readable and have a numerical scale, printed record, or digital readout in increments no greater than 2°F or over the intended range of use.