fun fact about the allegro gauge so finnish used the russian guage of 1524mm but when soviets updated it to 1520mm when modernizing their rail lines they didnt change it themselves either so the allegro ran daily between helsinki and saint petersburg and while the other russian connecting line (to moscow) did the normal slow and time consuming gauge changing procedurs the allegro trains were built for a nonexistant 1522mm gauge because they its halfway between the two and within the allowed tolerance of both (though i believe finland has higher tolerances iirc) so with only a 2mm difference from each they could run at high speed in both countries