Dew Point and Humidity calculations

These calculations are based on Vaisala's humidity conversion formulas.

*Note that measuring humidity accurately is challenging, especially at high humidities. Even the best
humidity sensors start to over read 1 - 3 % once you get past 90% RH.*

- Initially the Water vapour saturation pressure
`(P`is calculated:_{ws}) - Water vapour pressure itself is then calculated (hPa) using the relative humidity and
`P`_{ws} - Now Dew Point
`(T`can be calculated:_{d}) - For calculating dew point and humidity from the wet bulb (for a given pressure):

$$P_{ws}=A*10^{\left ( \frac{mT}{T+T_n} \right ) }$$

`T` is the temperature in deg C, the following are constants valid for a temperature range
-20 - +50 deg C with a maximum error of 0.083%; `A` = 6.116441, `m` = 7.591386,
`T _{n}` = 240.7263.

$$P_w = P_{ws} * \frac{RH}{100}$$

$$T_d = \frac{T_n}{\left [ \frac{m}{^{10}log \left (\frac{P_w}{A} \right )} -1 \right ]}$$

$$P_w = P_{ws}(T_{wet})-pressure * K * (T_{dry}-T_{wet})$$

where `P _{w}` = Water vapour pressure,