Legend panel:
"A stock-ticker style representation of how queries are moving over time. For example, if the time is 1:10pm, your time picker was set to "Last 10m", and the "Time Ago" parameter was set to "1h", the panel would show how much the query results have changed since 12:00-12:10pm"
Legends provides input for a single timeslot. Is it possible to draw a graph by comparing yesterday and today