Just a comment about estimating heights...
Some time ago I was a solo rated glider pilot. Got very used to making flights at between 1000 and 2000 feet on the flat in the UK. All our final turns were made about 350-400 and were mostly judged by eye. Then one day I went for a flight in the mountains of switzerland with an instructor and went a lot higher. On our return to the field my sense of altitude was shot. At one point I was convinced we were down to around 800 feet and couldn't understand why we were heading away from the high key point to over fly his house. I looked at the altimeter and was surprised to see it reading nearly 3000 feet. My point is that even when you are used to judging heights it's possible to be completly fooled.