A critical study of the conductance calibration standard, 0.01D aqueous potassium chloride solution, at 0°C, 18°C, and 25°C has been made using a highly precise thermostat and temperature program, a conductance measuring assembly of comparable precision, and a new type of absolute conductance cell. In spite of the high precision with which cell constants can be determined at any one temperature, the values at differents temperatures are only compatible with a linear temperature dependence within much larger limits.