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Standard baseline is a constant distance used to calibrate rangefinders. In Finland standard baseline is located in Vihti, Nummelanharju where it was built 1932. Gravel esker was chosen as measurement location soil since temperature variations cause very little displacement on benchmarks on which measuring devices are placed. In year 1947 white light interference based measurement system was taken to use. It was developed by Yrjö Väisälä. Before that baseline was defined by quartz made measuring rod, which was used to calibrate 24-meter long invar-wire. Standard baselines length is invar-wire multiplied by 36, which is 864 meters. Measured numerical value for 2007 for standard baseline in 2007 is 864 122,86 millimetres ±0,002 mm to ±0,007 mm uncertainty. 864 122,86 mm ≈ 864 m. Previously used quartz rod had 0,1 mm deviation from 1 meter – intended length – and it was taken account in new measurements. ==Sources== * (Interference measurements of the Nummela ) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Standard baseline」の詳細全文を読む スポンサード リンク
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