Zeal Precision Laboratory Thermometers are made from the highest quality lead, normal or borosilicate glass that has been specially selected to have a uniform capillary bore and to be free from strain. Instruments are scientifically annealed and artificially aged before calibration to ensure stability and maintain accuracy.
Top expansion chambers are provided where necessary to allow for overheating and to facilitate rejoining of the spirit column should it become separated in transit or use.

Thermometers with Blue, Red or Green non-fading spirit are pressurised internally and have pressurised nitrogen gas above the column to ensure reliable readings at the lowest temperatures on the scale.
Scales on most of the thermometers have Permanently Marked graduations, figures and naming.