The figure on this page is a Microsoft Excel (TM) table showing the results of our frequency count.
The gramophone sat in your parlor and certainly couldn't be carried along with you and your earbobs. When 78 rpm records first appeared on the market, they were very rare.
When they became popularly available, you could find them everywhere; but then the technology changed and they became rare again. Archaeologists investigate trash, not shop window displays, so we measure things when they are discarded; in this example, we're going to use junkyards.
Archaeologically, you would expect no 78s to be found in a junkyard that was closed before 78s were invented.
There might be a small number of them (or fragments of them) in the junkyard which stopped taking junk during the first years 78s were invented.
We count the types of musical recording methods found in each of our junkyard samples, and then work out the percentages.