You this is me: adjust fire, over. Request target description...
It's a slide rule.
Actually, it's that thing you're looking at. So it's sorta kinda like a slide rule, only you can't use it to do your taxes. Assuming anyone uses a slide rule to do their taxes anymore (fogy alert: I remember my father using a slipstick to do HIS taxes when I was a kid. His first calculator, a massive Texas Instruments desk model could actually add, subtract, divide and multiply! It was infinitely cool, for 1972..)
A GFT, as it's usually called, is part of what's termed "Manual Gunnery" by the Army schoolhouse at Fort Sill. A fire direction computer (that's a person, BTW) uses the GFT to index range to target for a certain propellant charge to determine the elevation of the gun barrel that will allow me (the FDC Chief) to provide data to the guns. There's actually a lot more of this stuff, like "site" and angle of site and complimentary angle of site (and this is just the up-and-down, long-and-short range thingies - what FA types call "quadrant" - I'm not even going into the left-and-right data we call "deflection") which allow you to spoil somebody's day several klicks over the next hill, but it's only of interest to FA geeks like me and ol' Harry Truman.
Why the hell call a blog "Graphic Firing Table"?
Well, in my experience, a GFT is a simple but useful tool that helps you to commit broadcast mayhem. Kinda like a blog.
Hope that helps. Don't hesitate to write me with all of your manual gunnery questions! I am sort of like Dear Prudence with a chart board...
End of mission. Out.