In canvas, how do I get the content of one chart and use it in another chart?

Hello, I have a question to ask, how does canvas get the content in the inserted chart?
As shown below, in canvas, how do I get the ordinate A of this bar graph and apply it to another graph?

Chart embedded is a canvas doesn't expose its internals to Canvas. You could however open the chart and see how A is being contructed and try to replicate it using available methods for canvas (query to ES, timelion etc)