iOS Calculator app with expression history feature, like Speedcrunch

I'd like to find a calculator app for iPad and iPhone (ideally a universal app) that supports entering expressions and retaining expression history and ideally also storing variables. I'm basically after the iOS app that is most similar to the desktop calculator 'Speedcrunch'
http://speedcrunch.org/en_US/index.html

Would be grateful for any suggestions anyone can offer

Cheers