Lesson plan

Optical square

The optical square uses a pentaprism to reflect and refract a beam or sighting 90 degrees, it is used in pairs in surveying and in a singular block in metrology. In optical square A Horizon glass is placed at an angle of 120° with the horizon sight. The Index glass is placed at an angle of 105° with the Index sight. Angle between Index glass and Horizon glass is 45°.

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Article summary

The optical square uses a pentaprism to reflect and refract a beam or sighting 90 degrees, it is used in pairs in surveying and in a singular block in metrology. In optical square A Horizon glass is placed at an angle of 120° with the horizon sight. The Index glass is placed at an angle of 105° with the Index sight. Angle between Index glass and Horizon glass is 45°.

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Discussion questions

  1. Summarise the article in your own words. Which single claim would you verify first, and why?
  2. Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
  3. If two sources disagreed about one of these facts, what would you need in order to trust one over the other?

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Key claims and bibliography are generated from the same tracked claims and sources as the article page.