I’m not sure there’s a global norm or scientist/hygiene recommended expiration date on sheets.  There especially confusion (for me, at least) around sheets in the guest room.  Do you only put on the sheets when they arrive?  How long can you leave the sheets on there before someone uses them or they need to be washed again?  Do you just wash the sheets or do you wash the blankets at the same time intervals?  Does it really just depend on who you are?

Do binoculars let people with great vision see further than people with poor vision?  I guess it’s more a question of how they work.  When you adjust them, are you sacrificing distance for quality?  Do our eyes focus on the image way off in the distance, or an image that is contained within the binoculars?