#2080: MirrorMeter

Today’s invention is a tape measure with two reels on board, as shown.

This allows the distance between two points (A and B) to be measured precisely without the casing (green) getting in the way.

It also means that by allowing the reels to slide into contact with each other, the tape when pulled from one side will emerge to the same degree from the other.

This would facilitate location of the mid point of AB exactly, which can be a useful time saver, especially within a restricted space.


  1. This is a very inspiring one!

    How about a mechanical adder that could add up “the two reels” automatically?
    (in digital world it is easier)

  2. Could the “adding” could be done mechanically with a differential gear?

  3. Besides the orientation “back to back” the reels could be on a single axis, doubling the width of the device iso the length..
    In the middle of that axis one could place a gearbox (differential?) to make the length visible?

    A variation could be the measure-blok to measure two orthogonal distances to calculate an area.
    And with 3 you could do the cube..

  4. If you were happy with reels in contact, you could have one with no markings and one with 1cm calibrations which were actually 2cm apart. Reading this one where the tapes meet would give the total distance between the end tabs…but I’m sure there is a more elegant mechanical solution that also allows independent use of the reels.

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