wooden box that could expand out the end to raise and lower
These were made by Hockema Signs in Hockema, Indiana in the 70s. He called them Adjust-a-stool.
I bought two at 35 dollars each. When I tried a couple years later to get another one he said he sold them all and wasn't going to make any more, but he sold me the hardware to make another one.
He has since passed away.
These are the only tools I have that are pushing forty years old. I used to stand on the high end till I stopped trusting my balance. I used to take it up on wall jobs, too, when I worked off pick-and-ladders. I could sit on the pick for one height of lettering, then sit on the box at several more heights, then finally stand. It allowed me to avoid having to awkwardly bend over, especially helpful if the ladders were a little shaky. And I could avoid raising the pick more times than I needed to.
The heart of the stool is a pair of spring-loaded pins, similar to the picture below, mounted to the inside box. The pins enter evenly spaced holes drilled into the sides of the outside box, holding the inside box at its various heights. A simple linkage pulls the pins inward when a ring is pulled up at the top of the inside box. I periodically rubbed the sides of the inside box with paraffin to keep the sliding action smooth.
The actual pins used have holes drilled in the little ball ends for attachment to the linkage that pulls them back. Other than that, the picture below looks just like them.
Brad in Kansas City