What's meaning of 10/350 µs wave and 8/120 µs wave ?

10/350 µs wave to characteristic current wave from a direct lightning strike (i.e. 10µs rise time and 350 µs voltage surge duration).
8/120 µs wave to characterise current waves from an indirect lightning strike (i.e. 8µs rise time and 120 µs voltage surge duration).

Released for:Schneider Electric Thailand