Question about the ski events

[Bayguy]

Hi this isnt about a specific sking event so I didn't put it under one of those threads, hope thats okay.

We're just watching the x-country skiing which is very pretty. Did you see the snowmen on the biathalon course the other day? Havent seen any yet today. Anyway, how do they get such acurate times for the skiiers? I thought maybe they have those little tags on their boots like runners use, but when theres a photo finish its who's ski crosses the finish line first not their foot. But the tag can't be on the ski because like in a little while these guys are going to change to different skis. They are showing 1/10ths of a second timings so tehre must be some kind of sensors on the track and on the skiers but I can't figure out how they do it.

Also on ski jumping, how do they know where the ski touched the ground? I dont think they have sensers under all the snow. 'Cuz they cant measure how far somebody went until they hit the ground.

Hope these aren't dumb questoins but we can't figure it out. Thanks!