4.0
The single prime, 4', does represent a length of four feet.
It means 4 atoms of Hydrogen.
The English term '4' has two different uses: 1: being one more than three; 2: the cardinal number that is the sum of three and one
In the musical time signature 4/4, the top 4 indicates four beats in a measure and the bottom 4 means each quarter note gets a full beat.