I've dealt with this recently. When something is triggered programmatically you have to initiate a trigger on that programmed event before you can do something. I believe what I did was this.

$(selector).trigger("change"); //The field to watch changes for. Here selector should be the calculated field element ID

Then:
$(selector).on("change", function(){ //Here selector should be the calculated field element ID
//What to do here
});

https://neoaz.net/bibs/

Using Bobby's idea, you can try adjusting the code like this and see if that works.  The code additions are in bold.

< script >
	jQuery(".myNum").each(function () {
		var j = jQuery; //Just a variable for using jQuery without conflicts
		var addInput = (this); 
		var n = 0; //n is equal to 0

		//Set default value to n (n = 0)
		j(addInput).val(n);

		//On click add 1 to n
		j(this).next("span").on('click', function () {
			j(addInput).val(++n);
			j("#field_qb04u").trigger("change");
		})

		j(this).prev("span").on('click', function () {
			//If n is bigger or equal to 1 subtract 1 from n
			if (n >= 1) {
			    j(addInput).val(--n);
			    j("#field_qb04u").trigger("change");
			} else {
				//Otherwise do nothing
			}
		});
	}); 
</script>

Thats perfect Thank you! As far as having the option to Edit from the front-endm What would I need to change for the code to "read" if there is anything in the fieldbox (as I read it in my limited capacity, the variable sets to 0. So if an entry is being Updated, it'll revert that to 0