Similarly, try drawing a 2 cm line with a 'real ruler'. Then, the line drawn with an ordinary ruler (top) was longer than the line drawn with a 'real ruler' (bottom) by about 0.3 mm in width of ...

Learn how to change Ruler unit in Word, Excel, PowerPoint from default inches to cm, mm, points, picas via Settings, Registry or Group Policy Editor.

Like a versatile ruler of light with tens or hundreds of thousands of closely spaced “tick marks,” an optical frequency comb provides exquisitely precise measurements of light.