Fuel reminder

I'm trying to make a mod and on of the blocks in it is a crusher. I have it set up like this, : 3 slots 0 is for the input item 1 is for the fuel(coal if it matters) and 2 is the output right now i have it setup so when you put coal in slot 1 it takes the coal and adds 1 to my variable "CrusherFuel" it will only take it if it meets these conditions its coal and my variable "CrusherFuel" is under 100. Here's my problem, i'm yet to add any thing else but before i do i want some sort of visual reminder of how much fuel there is but im not sure how as the GUIs text label cant change and there's no sort of progress bars. Can anyone help? If so Thanks!