When signed into my blog, this graphic is up on top. I know it shows visitor pattern over 48 hours, but does anyone know what the number represents? I searched on the WP site, and am not finding this.
When you sign in, You can see tiny site stats chart(displayed in above screenshot) in your toolbar called a Sparkline.
The number in Sparkline represents the highest number of visitors visited in 48 hours of day.
You can find more information in wordpress.com Stats Support.
I have copy pasted the content below from this link so that it will not affect if that link ever changes its content in future.