Each of the DewPt apps computes a dew point from old fashioned wet and dry bulb thermometer readings. No internet access is needed.

They compute the dew point temperature and relative humidity from an input wet bulb temperature, dry bulb temperature and barometric pressure. Often a barometric pressure guess of 29.8 inches of mercury or 760 mm of mercury gives a near enough result, so often a barometer is not necessary.

They use a computation method suggested by the National Weather Service of the National Oceanic and Atmospheric Administration, USA.

Abbreviations are:

• ‘degrees F’ means degrees Fahrenheit.
• ‘degrees C’ means degrees Celsius.
• ‘Inches Hg’ means inches of mercury.
• ‘mm Hg’ means millimetres of mercury.

On mobile devices black text that has a blue glow indicates a number that can be edited. A tap on such a number will change the glow from blue to green and a virtual keyboard will appear in the lower part of the display. Generally the keys affect the right hand end of the number except the “+/-“ key which toggles a minus sign on and off at the left hand end. If a positive number is required the “+/-“ key is not visible. If the number contains a decimal point the decimal point key is not visible. This ensures that the number has only one decimal point.

A red glow indicates a number that is not valid. Any action that takes the focus away from that number will cause it to return to a previous value; the editing being ignored. A tap on the Enter key will make an error message appear.