pH readings vary with temperature. For example, a sample with a pH of 7 at 77 F Celsius will have a pH of 7.08 at 41 F and a pH of 6.98 at 140 F. You can either adjust for the difference manually or have the compensation adjustment made automatically by buying a pH meter with ATC. pH meters with ATC have a thermometer built in so you can usually use the meter as a thermometer also.
