r

HTML

<span id="num">0</span> <br>
<span id="incSpeed">(+0/s)</span>
<button id="btn">
increase
</button>

JavaScript

let num = document.getElementById("num");
let btn = document.getElementById("btn");
let Increment = 0;

function toIncrease (){
    Increment += .1;

    if(Increment == .1){
    setInterval(()=>{
        num.innerHTML = parseFloat(parseInt((parseFloat(num.innerHTML)+.05+Increment)*10)/10);
    },1000)
}
}

btn.addEventListener("click",toIncrease)