traveler's calculations

you know that you travel a lot when you know exactly how long it takes you to go through your various toiletries - but only the ones that you can't buy overseas. i know how long my contact solution lasts, and conditioner and lotion-with-SPF, because i can only buy the brands i like in the US. i have absolutely no idea how long my toothpaste or shampoo lasts, because i can buy them anywhere.