Use archive.org link for humidity conversion formulas, fixes #73

MEASUREMENTS.md

@@ -44,4 +44,4 @@ For the purposes of blacklisting or whitelisting the values, the table below dis
 
 ### Calculating extended values
 
-All extended values are calculated in [MeasurementValueCalculator.java](./src/main/java/fi/tkgwf/ruuvi/utils/MeasurementValueCalculator.java). Unfortunately I've lost the original sources for most of the equations, but with a little searching similar ones can be found, such as [this](https://www.vaisala.com/sites/default/files/documents/Humidity_Conversion_Formulas_B210973EN-F.pdf). Needless to say, the extended values are rough approximations, sufficient for the average home user. For scientific use, you should disable the extended values and use your own scientifically accurate formulas.
+All extended values are calculated in [MeasurementValueCalculator.java](./src/main/java/fi/tkgwf/ruuvi/utils/MeasurementValueCalculator.java). Unfortunately I've lost the original sources for most of the equations, but with a little searching similar ones can be found, such as [this](https://web.archive.org/web/20180116050920/https://www.vaisala.com/sites/default/files/documents/Humidity_Conversion_Formulas_B210973EN-F.pdf). Needless to say, the extended values are rough approximations, sufficient for the average home user. For scientific use, you should disable the extended values and use your own scientifically accurate formulas.