Not directly watch related but I thought I'd let people know. To anyone who's going to Japan to buy watches during summer, you should avoid any sports drink that claims to protect from heat illness, including the popular pocari sweat. You should opt for pic related instead. It's comparatively expensive at around 220¥ and it's not available in vending machines (that's why it probably works) but it's your best bet to avoid any dizziness and ir even cures hangovers.
Take care.