21 CFR § 112.124 - What requirements apply to instruments and controls used to measure, regulate, or record?
Instruments or controls you use to measure, regulate, or record temperatures, hydrogen-ion concentration (pH), sanitizer efficacy or other conditions, in order to control or prevent the growth of microorganisms of public health significance, must be:
(a) Accurate and precise as necessary and appropriate in keeping with their purpose;
(b) Adequately maintained; and
(c) Adequate in number for their designated uses.