Error: ambiguous reference to overloaded definition in Scala function



Hi I am writing a function that takes an Iterator as an input and returns the sum of revenues, below is the code I wrote for this

def getSum (productVal : Iterable[((String, String, Float), (String, String))]) : Unit = {
var revenue:Float = 0;
for(products <- productVal)
revenue+ = products._1._3

but when I paste it in spark-shell I am getting the below error:

:31: error: ambiguous reference to overloaded definition,
both method + in class Float of type (x: Char)Float
and method + in class Float of type (x: Short)Float
match expected type ?
** revenue+ = products._1._3**

any idea what am I doing wrong here?