Abstract: An elongated container, open at end, is nearly filled with frozen fluid. Urethane foam insulation around the container admits access only to the open end of the container with the frozen fluid level below the insulation. An elongated heat conducting indicator member fits loosely within the container so that fluid may pass therebetween. An elastic band over the end of the indicator/conductor and around the base of the insulation maintains an end of the indicator/conductor in contact with the frozen fluid. The indicator/conductor is calibrated in degree-hours or other temperature-time units. The indicator/conductor may be a hollow flat-bottomed tube with air inside acting as the heat conductor from the exterior air to the contact end of the block of frozen fluid.