Very good windows desktop calculator by LucBigjohn
https://docs.google.com/file/d/0BxGcL1JOoEcyb2JRUGNKUFZpSDg/edit?pli=1
https://docs.google.com/file/d/0BxGcL1JOoEcyb2JRUGNKUFZpSDg/edit?pli=1