Creating a new rate (no replies)

I'm trying to create a new rate in my plugin. I have created a class that extends the Processed Metric class and created a public function format that return $formatter->getPrettyPercentFromQuotient($value); Everything seems to be working great until I hover over a date in the Evolution graph. My rate is not formated with a % sign. I have tried to set everything up like the BounceRate, but all I'm getting is just a number without the % sign. When I look at the HTML code, it looks like format is missing the & sign where yaxis is BounceRate and y2axis is my new rate. "yaxis":{"tickOptions":{"formatString":"%s%"}},"y2axis":{"tickOptions":{"formatString":"%s"}}}

What other setting should I set?