Thousands of years after it's invention, the humble compass continues to be the best way to draw a circle. And divide a circle. And bisect a line. And almost every other geometric tasks. For those looking to plan and design by hand or work with radiused curves, the compass is a must-have.

This particularly nice example from Shinwa comes with an extension arm, which can be used to extend the possible circle sizes available.

Using it's pair of standard arms, the maximum useable radius is about 130mm.

By attaching the extension arm, this is extended to 200mm - and can be pushed to 250mm if both arms are angled to their maximums.

• Size: 120x13x10mm
• Material: Body / Screw: Brass chrome plating. 
• Contains 4x 2mm leads (30mm long)
• Country of origin: Japan
• Specifications: Radius: Up to 200 mm (Maximum radius when using relay shaft: 250 mm)
• Shinwa Rules Co., Ltd. (Shinwa Sokutei) is the leading manufacturer of measuring instruments having the largest share in Japan in the field of metallic scales.
• Made in Japan