What would be the process to do that? To aim 0 and 100 properly, you'd need a tool to calculate a 100:28 (25:7) ratio on an arbitrary distance, wouldn't you?
One can build such a tool, but it's not a doubled-over piece of string.
One can build such a tool, but it's not a doubled-over piece of string.
- get some string
- measure a length between your low and high points
- fold it in half
- make a mark at the halfway point of the string
- fold it in half again, etc.
No candles, projection, transparent or slotted ruler, wall, or carefully moving one's hand back and forth under projected magnification needed. Just some string.
I don't see how you're going to use this system to effect repeatable markings on glass tubes.
Try it: it's easy. Use a flashlight from your phone instead of a candle, then project light to a wall, then put your palm in the front of the light.