If you have a Windows Phone smartphone then you can download the Aura Toolkit mobile app for FREE. It is intended to complement your Aura spinning wheel and includes spinning recipes, specifications and an interactive tool that helps calculate the rate of yarn draw and twist for each of the pulley/belt settings.
You can see a selection of screenshots below and there is a direct link at the bottom of the page to the app in the Windows Phone Marketplace.
The link to the app is immediately below. Enjoy!