# Scaled Polydrafter Tetrads

## Introduction

In plane geometry, a *tetrad* is an arrangement of four congruent
shapes in which each borders the other three.
See Polyform Tetrads.
At his website Atlantis, Dr. Karl Scherer introduced *similar*
or *scaled tetrads.*
These are arrangements of four geometrically *similar*
figures in which each borders the other three.
That is, they have the same shapes but not the same sizes.
In general, scaled tetrads are easier to find that standard tetrads.

A *polydrafter* is a polyform whose cells are right triangles
with angles 30°, 60°, 90°.
It is half an equilateral triangle.
Polydrafters whose cells do not conform to the underlying
grid of equilateral triangles are called *extended* polydrafters.
For example, there are six proper didrafters and seven more
extended didrafters.
See Bernd Karl Rennhak's site Logelium
for examples.

Here I show the smallest known scaled
tetrads for polydrafters with 2 or 3 cells,
using a common orientation for the cells, and
using scale factors that are integers or integer multiples of √3.
If you find a smaller solution or solve an unsolved case, please write.

## Didrafters

## Tridrafters

Last revised 2020-05-08.

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Col. George Sicherman
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