DESCRIPTION OF EQUIPMENT 
The new NEL calibration tank (fig. 1) represents 
an improvement over the earlier designs in that it 
provides automatic temperature control, very high 
accuracy, rapid operation, and a simplified method 
of taking readings. The NEL tank will also calibrate 
twenty-four thermometers at a time, or twice as many 
as possible in previous models. These thermometers 
may be moved into position after their temperature 
has equalized with that of the tank and read in situ 
by means of a reading telescope. The tank is well 
insulated from ambient temperatures so that little 
addition or subtraction of heat is necessary to main- 
tain temperatures within the desired limits of ac- 
curacy. The rate of heating and cooling is controlled 
precisely, permitting rapid large changes of tempera- 
ture, accurate microchanges of temperature, and 
maintenance of temperature within very small limits. 
Figure 1. Controlled-temperature calibration facility. 
