Applying decimals

[AlwaysVbNet]

I am trying to apply a decimal rating i.e. 2.3 but it won't display the correct result. I'm using knockout.js.
Any ideas how to fix?

var rating = ko.observable(2.3);
var options = {
values: [1,2,3,4,5],
allowFractional: true,
calculateFractional: function (current, rate) {
if (current.indexOf(rate) === 1) {
return 0.6
};
return 1;
},
allowFractional: true,
readonly: true,
applyHoverCss: false
}

I did this which works but how would you apply decimals without my edit?
calculateFractional: function (current, rate) {
if (current - rate > 1) {
return 1;
} else {
var x = current - rate;
return 1 + x;
}
},