Based on a previous question asking about mechanical computing (Babbage engines, etc.) I wondered how a steampunk story could present the concept of a modern computer monitor in a steam-driven mechanical world.
Background: While pondering the problem of shrinking or otherwise utilizing mechanical computers, I wondered if their most limiting attribute wouldn't be the display monitor. You could meet the basic expectations of suspension-of-disbelief with a pocket-watch sized computer (the small watch gears, densely packed and spring driven, whirring away inside. Let's not worry about heat.). But what would I be looking at?
When my eyes were younger, I could comfortably read 6-point Times New Roman text. Printing a wheel with minimum inter-character spacing having 26 letters, 10 numbers, and maybe 10 punctuation marks (including the space), means a wheel with 46 minimally-spaced characters. The diameter of the wheel would limit actual character spacing on the "display" (the space between the characters I read would be equal to the diameter of the wheel). I could reduce that by half if I'm willing to live with letters that jump up and down, allowing me to interdigitate the wheels.
But, in the end, there's simply no efficient way to display text in this manner. I could use something like the old 1970s-era bedside clocks that flipped panels. But 46 characters would require 23 panels, which feels mechanically yucky (and so very 1970s...).
Idea: I propose for a steampunk universe a very small cylinder, it's height equal to its diameter. The cylinder is painted in five1 shades of white (creating a spectrum from white to black). Kinda like this:
The mechanics would spin this sucker around at a thousand miles per hour, pausing briefly whenever a color must be displayed. My pocket watch may have a "display" of 30x30 small spindles, allowing text to appear to scroll across the screen.2
Clarification: in pixelated displays, everything is a graphic image. True, in the early days of computing dedicated hardware converted the concept of the letter "A" into the picture of the letter "A," but the distinction is one of advancement, not discovery. If the make-or-break point for the believably of the idea is moving pictures and not simply scrolling text, moving pictures are an easily dispensed with concept.
Due to the spinning, the background color of the "monitor" would be the average of the colors on the spindle (which argues against using an odd number of colors) or 50% black.3
Theoretically, the cylinder can be made of a small enough diameter to produce a reasonably smooth, if rough to look at (you'll be wishing for that 8-color TRS-80) pixel display.
Clarification: using a modern reference for pocket watch sizes, the largest watch is about 16mm or 2.3 inches. Accounting for the glass size, let's assume 1.5 inches with a 30x30 pixel display for 20 dpi. Technically, the letter "H" could be made 4 pixels wide (including white space for the next letter) and 3 pixels high, but it's not the most complicated letter. Ignoring whether or not the display could believably scale text, let's assume 8-pixel-tall letters in three rows separated by some pixels for legibility. Remember, however, that as a pixelated display, it's only limited by the technology driving it. This question is more about the believably of the display than it is whether or not you can make a purely mechanical graphics card.
Ignore the fact that 99% of the mechanics in a pocket watch and far too much of a "table top" mechanical computer would be given over to interpreting and processing display information and the control of the display.4
Ignore the fact that such a solution would last a very short time before breaking.
Ignore the fact that you'd need ear muffs to (literally) muffle the sound.
Ignore the fact that the gearing itself may take too much space to permit a comfortably dense display.
Ignore the size of the spring required to drive this. At the moment, it's being stored in an attached pocket universe and you'd need a modern power drill to wind it up.
Question: For a steampunk story, would the presented display appear too modern, out of place, to too mechanically unsound — or would it fit neatly into the "modern conveniences in a steam-driven society" that is the steampunk world?
Clarification: If you're familiar with the American TV show, The Wild, Wild West (the original TV show, not the horrible movie), then imagine Artemus Gordon flipping this watch open to help Jim West save the day with some critical piece of info from Washington D.C.
1 Frankly, you could paint 256 colors. The problem is that you need a wide enough mark on the cylinder to be visually discernible during use while keeping the diameter of the cylinder to an absolute minimum for maximum "screen resolution." I'm having trouble convincing myself that even 8 colors would work. 5 might be a stretch.
2 Part of my inspiration was an episode of the Murdoch Mysteries that used grayscale to transmit a photograph of a mystery woman to the constabulary. If only they had this device....
3 You could change the behavior to "park" on white or black and only "spin" to the color that's needed in any given moment, but that's a lot harder than "pausing" while spinning. Ultra-high-speed printers in the 70s and 80s used a drum filed with spirals of characters that constantly spun with hammers that struck the paper against the drum to print. It's fast and efficient — but not quiet.
4 If you don't believe this, please take the time to look up the processing requirements to convert "computer-speak" (electronically: binary) into the beautiful letters and pictures you see on your monitors today. The actual electronics involved in that process is substantial. Doing it mechanically may be DaVinci-esque and cool — but I'd hate to be the one to design and build it.