Stop text in a label with changing numbers from changing width in swift IOS

Question

How do i stop text in a label from moving/changing size (being dynamic) when it has numbers that are changing every second.

var duration = //user input
func counting() {
    label.text = "\(duration)"
    if duration > 0 {
        duration -= 1
    } else if duration == 0 {
        //stop
}

The functions updates itself every second.

I have an label that have numbers counting down every second, but when it changes numbers the width changes to depending on how big the number is. How do i stop this and give every letter/number the same width. So i want an "1" to take as much space as an "5". I am not talking about the space between (margin) but rather the space inside (item/letter/number size).

Label text taking more space then if it had been 4:11

Label text taking less space then if it had been 3:56

Answer 1

After checking out monospaced fonts after a tip from @Yuri i have found a solution.

Here is an another question that shows you have to add monospace to a label in IOS 9, that i successfully fixed my problem with.