Unit conversion library for .NET

I have had a great time learning F#. I wanted the experience of making a simple, high-quality F# library to get some practice.

Let's talk about units for a minute. What is a unit of measurement? Well, it's a way to express a quantity. The SI System defines units for these quantities:

• electric current
• temperature
• time
• length
• mass
• luminous intensity
• amount of substance

Converting between two units can be done with a function where the values of the parameters are determined by the source and target units. For a quantity like temperature, 0ºC is not the same as 0ºF. Perhaps you have seen the function to convert from Celsius to Fahrenheit:

let convertToF degreesC = 9./5. * degreesC + 32.

Converting between two different units of measure for the temperature quantity must take an offset and a slope into account. So, we have a function to convert between 2 different specific units in a single direction. To perform the opposite conversion, we need another function.  C --> F F --> C For 2 units of measure, we need 2 functions. Saw we want to add Kelvin (K) to the mix. Now we have: C --> F, C --> K F --> C, F --> K K --> C, K --> F For 3 units of measure, we need 6 functions. How about Rankine (R)? C --> F, C --> K, C --> R F --> C, F --> K, F --> R K --> C, K --> F, K --> R R --> C, R --> F, R --> K

For 4 units of measure, we need 24 functions. I'm not writing those. That's n factorial functions! For length, 0 is 0 is 0. Said another way, 0 US Survey Feet is the same as 0 meters. Perhaps you're thinking of the y = ax + b from school. In the case of length, there is no 'b' or offset term, just different slopes, 'a'. So, what would such a function look like?  let convert value source target = value * source / target Let's talk about length. Some common units for length are the meter and the US Survey Foot, defined as 1200/2927 meters https://en.wikipedia.org/wiki/Foot_(unit)#US_survey_foot. Is 0 meters the same as 0 feet? Yes, it is. Length is nice in that two different length units differ only in their slope, not their offset.