On this day in 1889 the first General Conference on Weights and Measures defined the length of a meter as the distance between two lines on a standard bar made of platinum with 10% iridium measured at the melting point of ice. The bars were cast with an X-shaped cross-section to minimize torsional strain when bars were measured side by side. The standard endured until 1960, when it was replaced by 1,650,763.73 wavelengths of light from a certain transition in krypton-86.
