Helix - 2-in-1 Ruler - Integrated Circle Templates - Innovative Learning Tool...

3 in 1 Ruler and Compass for Kids Draw Circles Up to 12 Inches with Graduations

Helix Angle & Circle Maker

3 in 1 Ruler and Compass for Kids Draw Circles Up to 12 Inches with Graduations

Helix Standard Ruler, 12 Inch / 30cm, Assorted Colors (13105)

Helix - 2-in-1 Ruler - Integrated Circle Templates - Innovative Learning Tool...

3 Vintage Rulers Including Engine Divide By Hall Harding Ltd, Helix No. 21/28