Very good explanation given by Tinstaafl. I'd never thought of the "long elastic" analogy. In my dim and distant youth as a military trainee pilot, we were given these aphorisms for use when thinking of altimeters and how accurate they might be.
"From warm to cold, don't be bold" to cater for the temperature effect described by Tinstaafl.
"From high to low, careful go" to warn of reduction in actual altitude when flying towards a region of lower pressure without adjusting your altimeter's subscale.