Adjusting The Needle of Speedometer Chart

Hello All,

I am creating a dashboard that will show someone's quality in a single quick glimpse. I have been able to create the speedometer look and am quite happy with it. With that being said, the needle moves on a percentage base from 0% to 100% accordingly. However, 90% of the quality results are greater than 50%, and so I am trying to show the 180* view but from 50% to 100%. So if the needle is at 9:00 it reflects 50%, 12:00 it reflects 70%, and 3:00 reflects 100%. After hours of trial and error I am unsuccessful. IF this is possible, what adjustments do I need to make? Thanks for your help!!!