Two things. Your second condition for the button
else if (newSystem = "Metric") should be
else if (newSystem == "Metric"). It was missing and equals sign.
var newSystem = $("#btnChangeSystem").text(); is not assigning
"Imperial" it is assigning
"Imperial " with extra trailing space at the end. You could fix that by editing your html to take out that space.
Looking at it this more it seems your HTML doesn’t reflect that empty space but chrome dev tools does and if you console log the variable
newSystem after it is declared you can see the trailing space.
Edit: Just found that you misspelled button as botton in your HTML which when corrected seems to get rid of your extra space error.