You can use the Solver application of the HP CALC to find the distance in miles between two points on earth. In fact, the 95LX, 100LX and 200LX manuals all give an example of this equation:
DISTANCE=69.0466*ACOS (SIN(HR(LT1))*SIN(HR(LT2))+ COS(HR(LT1))*COS(HR(LT2))* COS(HR(LG1)-HR(LG2)))
Where LG1 and LT1 equal the longitude and latitude of the first place and LG2 and LT2 equal the longitude and latitude of the second place. The example is in the 95LX User's Guide: 30-18; 100LX User's Guide: 30-42; 200LX User's Guide: 30-32
David Shier CompuServe ID: [75030,3374]
[Editor's Note: You can find the Latitude and Longitude for major cities in WorldTime cities list on the 100/200LX.]