how to make float sum calculation?

am I doing the addition wrong? The result does not give the total number

public float GetGrandTotal(UtilizationDto issues)
        {
            var grandTotal = 0.0f;
            grandTotal += (float)issues.PercentCalculation;
            return grandTotal;
        }

>Solution :

Just declare your grandTotal variable in global and on each call it will not reset 0

public float grandTotal {get; set;} = 0.0f;
public float GetGrandTotal(UtilizationDto issues)
{
     grandTotal += (float)issues.PercentCalculation;
     return grandTotal;
}

public float Main(){
    GetGrandTotal(new UtilizationDto { PercentCalculation= 1.0f});
    GetGrandTotal(new UtilizationDto { PercentCalculation= 2.0f});
    return grandTotal;
}