Simplify the following text for a Grade 20 native English-speaking person.
Original: Four different major rail gauges ( which measures the distance between rails ) exist across the continent : most of Europe , as well as Turkey , Iran , China , and the Koreas use the 1435 mm gauge , known as Standard gauge ; Russia , and the former Soviet republics use a 1520 mm gauge ; Finland use a 1524 mm gauge ; most of the railways in India , Pakistan , Bangladesh and Sri Lanka use a 1676 mm gauge , and most of Southeast Asia has metre-gauge .
Simplified: There are four different major rail gauges ( to measure the distance between rails ) across the continent : most of Europe , as well as Turkey , Iran , China , and the Koreas use the 1435 mm gauge , known as Standard gauge ; Finland , Russia , and the former Soviet republics use a 1520 mm gauge ; most of the railways in India , Pakistan , Bangladesh and Sri Lanka use a 1676 mm gauge , and most of Southeast Asia has metre-gauge .