Abstract: Apparatus for determining and displaying the temperature of a mixture of two liquid streams, such as hot and cold water mixed in a shower supply line, includes a flow control valve for varying the flow rate of the mixed water independently from adjustment of temperature mixing and control valves. The apparatus includes structure for more uniformly mixing the two streams and for providing improved homogeneity of temperature in the mixture. A baffle is provided at the inlet of the device for redirecting the incoming mixture to a mixing chamber prior to exposure of a thermometer thereto. The flow control valve increases back pressure at the outlet thereby further to improve temperature uniformity of the outlet stream. The apparatus may be installed intermediate existing plumbing connections and does not require the use of specialized shower heads.