1. Did you try twisting the bulbs to see if they are socketed? Or try to push the bulbs up from theie "boots" to expose the wire/bulb soldering? The "boots" would have been impossible to install into the bracket with the bulbs in place, so either they had to have a socket to screw the bulb into after the boots were installed in the bracket or the bulbs with wires soldered in place would have been pushed through the installed boots and so should be able to push back up (unless there's some sort of hook/tab to prevent the bulbs/wires to be reversed [uninstalled]).

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2. The traces don't look like they vary in width to me. Except at the end of each trace, where they approach the terminal, the look pretty consistent in width. I think it's an optical confusion because of the waviness to the traces on the board.

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3. The keyboard switches look like "momentary on" switches. Are they?
   My guess on the mesh in front of the digits, was because they believed they were shielding from radiation (or glare).

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4. the memory bulb was possibly pushed through the rubber mask before the mask was mounted because then the space would be correct size to fit into the metal bracket. then the bulb wires were connected and wrapped with the grey stuff.

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5. The additional mesh is probably to avoid the numbers turning momentarily invisible when manipulating the red tabs. I had a VCR with VFD that went blank for a moment when I rubbed the hand on the front.

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6. I just saw one of those piece of garbage calculators sell on ebay for 500 dollars. Its like those rusted classic cars that should be crushed. Seriosly VFDs are inferior technology. Someone quick 3D print these displays in plastic fill the segments with semi-tansparent epoxy and put surface mount RGB leds on the back.
   Ok, now that I said it, It will be available on aliexpress within a month.

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7. Looking at those indicator lights, perhaps the glass part and wire pull out through the back of the socket. A touch of light lubricant in the rubber cup might seep in enough to let it be pulled out (the "Memory" bulb, of course).

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8. No draftsman would “hand draw” this complicated circuit board traces, it is tape. The waviness is from laying the pinstriping tape down. Plus the drawings are enlarged/shrunk as needed, if you shrink a drawing this could contribute to the effect you are remarking about.

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9. so no arithmetic logic unit. I'm guessing when you pressed a key that number was added to memory then the next key would multiply that number by 10 and put the new number where the old one was. then you push equal and that total gets moved to another memory and as you type more numbers the original memory is started from zero. now to add you just increment from the second memory to the first memory till the second memory is zero. I have a hunch it didn't handle floating point arithmetic. LOL.

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10. First time a circuit board reveal has ever made me swear out loud. 😄 Holy cow, that thing is packed! Who'da thunk the unique "Japanese brushstroke segment" tubes wouldn't've been the most fascinating thing to see here. Wild to see the ton of splayed legs on those alien-looking multi-flipflops (?), too. Interesting that the Iseden display tubes supported floating commas in addition to the periods, but Sharp didn't use 'em. Guess they plum ran out of space for driver circuitry!

    A side-benefit of leaving comma display to those sliding red plastic tabs is that the calculator would be able to display digit grouping both in Western 1,000-based grouping or East Asian 10,000-based grouping.

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11. I'm old enough to remember when they came out with adding machines with that type display (Nixie tubes?)
    I thought it was amazing.
    Ten years later they had pocket calculators with LED's and those were expensive paperweights.

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