An example for unfamiliar folks.

Many Languages

  var lengthInFeet = 2;
  var weightInKg = 2;
  
  var sum = lengthInFeet + weightInKg; // Runs without issue but is an error

F#

  [<Measure>] type ft
  [<Measure>] type kg
  
  let lengthInFeet = 2<ft>
  let weightInKg = 2<kg>

  let sum = lengthInFeet + weightInKg // Compile time error

More info at https://fsharpforfunandprofit.com/posts/units-of-measure/