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Nummela Standard Baseline

The Nummela Standard Baseline is a measurement standard for length measurements in geodesy. The lengths between observation pillars range from 24 m to 864 m. The baseline was established in 1933 for calibrations of invar wires. They were used to determine the scale of mapping in Finland. Since 1947 the FGI has measured the baseline 15 times using a Väisälä comparator, based on white light interferometry. The length of the entire baseline has varied only 0.6 mm in 60 years. The measurement result in year 2007 was 864 122,86 mm ±0,07 mm. The scale is traceable to the definition of the metre.

The long history, favourable environmental conditions and extreme accuracy have made the baseline internationally renowned. Nowadays the most accurate electronic distance measurement instruments are calibrated at the Nummela Standard Baseline. Using them the scale has during the last years been transferred, for example, to Estonia, Lithuania, Austria, Germany, Spain, China and South Korea. The baseline also serves in testing of new absolute distance measurement instruments.