Solution:

NumberFormatInfo formatInfo = new NumberFormatInfo();
    formatInfo.NumberDecimalSeparator = ".";
        
    if (IsPost) {
        var errors = false;
        var zoomstring = Request["Range"];
        if (zoomstring.IsFloat()) {
            zoom = float.Parse(zoomstring, formatInfo);
        }
        else {
            errors = true;
            @:Range - floating point number required.<br />
        }