Rather than carry another device, I use RealCalc [0] on my Android phone.  It supports RPN.<p>Besides, my HP-16C still works :-)<p>[0] <a href="http:&#x2F;&#x2F;www.quartic-software.co.uk&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.quartic-software.co.uk&#x2F;</a>