Just note Finland uses the Tsarist Russian 1524 mm gauge. Not the Allied Soviet 1520 mm gauge.
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The 1520mm was some Soviet effort to "metrify" their railways while keeping compatibility with existing rolling stock.
I also remember reading a long time ago that there were two engineering schools: one modeled that tighter tolerances would decrease oscillations and vibrations and the other predicted exactly the opposite. I think in the end they settled on natural experiments. Hope I didn't make this up, need to search for sources.