Some time ago I dreamt that I was in an alien space ship for some reason. Still carrying my phone and laptop bag. They were a friendly lot and asked whether or not I would like to charge my laptop. Do you have 220V sockets I asked. They didn't know what that was. So I needed measurements and definitions. An approximate meter, an approximate second. Coulomb was difficult. I woke up and downloaded Wikipedia the next day. Deleted it again later for lack of harddisk space...

But next time this happens I will have an USB stick with all the necessary knowledge. The definitions for voltage, current and frequency should however be printed out in case my laptop battery charge is insufficient for accessing the USB stick.