[David L.]

Let's take it a bit at a time.
You understand what 'pick the pencil up' and 'put the pencil down' mean. So let's look at 'upper' and 'lower'

In the front of a Jumbo, there are two passenger decks. You have to go up some stairs to get to the upper deck, and 'upper' distinguishes it from the other deck, the deck that you walk on to when you enter the plane. In relation to the upper deck, this deck (the one as you walk on to the plane) is located at a level in the plane lower than the top deck, and so is called the 'lower' deck.


'upper' as a noun refers to a layer of leather in shoes. There are two layers- a top layer and a bottom layer. In relation to each other, one piece is upper, and one piece is lower (in the shoe). Also, in false teeth (dentures), those that go in the top part of the jaw are called 'uppers', and those that go on the bottom of the jaw are called 'lowers.' This is a short way of saying, 'the upper set of teeth and the lower set of teeth'. (With drugs, colloquially some drugs are referred to as 'uppers' because they elevate the mood, cause one's mood to go up. Those that make a person's mood go down are called 'downer's.)
So : the upper deck is situated higher in the plane than the lower deck. The lower deck is situation lower in the plane than the upper deck.

OK so far??