Updating a label based on the sum of 2 value boxes

In this example we update a label to display the sum of two value boxes. The value boxes are linked to two distinct tags and utilize the "OnEndValueChange" function. 

double value1;
double value2;
 
void UpdateLineTotals(){
Label1.Text = (value1 + value2).ToString("N2");
}

public void ValueBox1_EndValueChange(object sender, Tag tag, DateTime timestamp, TVQ tvq)
 {
 double number;
 if(double.TryParse(tvq.Value.ToString(), out number)) {
 value1 = number;
 UpdateLineTotals();
 }
 }
 
 public void ValueBox2_EndValueChange(object sender, Tag tag, DateTime timestamp, TVQ tvq)
 {
 double number;
 if(double.TryParse(tvq.Value.ToString(), out number)) {
 value2 = number;
 UpdateLineTotals();
 }
 }