Digital Tachometer Modification

Adding a *constant on* feature.

I have wanted one of these for some time now but I need one that will stay on without holding down a button.  The ability to set the tool, leave it and say start or rev something then come back to it and know the max/min speeds is very useful for someone who works alone.  This was EASY, anyone can do it and in my opinion it makes for a much more useful tool.