Thanks to independent iOS and Mac developer James Thomson, you can now wear PCalc on your $400+ Apple Watch. The award-winning $9.99 calculator app for the iPhone and iPad was updated today with WatchKit support.
The app is very nicely done and feels native. It puts the full calculator with RPN Support on your wrist, along with a Glance to see the result of your most recent calculations from your watch face, a tip calculator and other goodies.