Increasing temperature in an aqueous liquid system results in a decrease in liquid density and an increase in vapor density. When level is measured by the differential pressure method, temperature increase results in a decrease in the effective span f the instrument and a shift in zero. When the instrument reference leg is uncompensated, both zero and span shifts occur with the effects being most pronounced at the high levels. When the reference leg is compensated, zero shifts are eliminated (instrument zero is at 100% level for this type installation). For control purposes at levels above 50% of full level, the compensated reference leg installation will give the best results. For measurement of levels below 50%, the uncompensated installation is best. As errors in level indications will be produced, in either type installation, by temperature, pressure and steam withdrawal (power) effects, the placement of taps should be such as to place the normal or control level in the region of 50% indicated level.