Dewpoint

Dewpoint is derived as follows:
exp(x) is the exponent function, the constant e raised to the power (x).
e_sw is the saturation vapor pressure over a plane surface of water.
e_vp is the vapor pressure

e_sw = 6.1078 *
       exp(5.0065 * ln(273.15/kelvin_temperature)) *
       exp(24.846 * (1 - (273.15/kelvin_temperature)))

e_vp = (humidity/100) * e_sw

dewpoint = (237.3 * ln(e_vp/6.1078)) / (17.27 - (ln(e_vp/6.1078)))