Von der RM Website:

"Alexander Zverev now plays with a Richard Mille watch on his wrist. For this right-handed player who is extremely powerful in his game whilst being comfortable on any surface, the RM 27-01 is the ideal timepiece, with its case made of carbon nanotubes, weighing 18.83 grams, inclusive of the strap -a world record for a mechanical watch- yet to be matched.
Developed hand in hand with Rafael Nadal, the tourbillon calibre suspended by cables can resist accelerations of up to 5,000g’s. Designed for tennis, this watch feels like a second skin."