java string cannot be converted to boolean error

You are currently assigning the value M to SystemOfMeasure, but if or else if conditions expect a boolean expression, NOT an assignment.

So, you need to use .equals() method (which returns true/false) for string comparisons like SystemOfMeasure.equals("M") as shown below:

if (SystemOfMeasure.equals("M")) {
     //add your code
} else if (SystemOfMeasure.equals("I") {
    //add your code
} else {
    //add your code
}

Also, remember that, you need to follow the java naming standards like lower case for variable names like systemOfMeasure