Distance and Direction for the HP-32SII

Written by Dave Coffin around 1992.

Overview

This program calculates the distance and initial heading of the shortest path between two points on the Earth's surface.

Usage

A Moslem must always face toward Mecca during prayer. Which way should a Moslem in Boston face?

XEQ D
N? 42.3566	Downtown Boston
E? -71.0569     Always negative in USA!!
N? 21.426	Mecca, Saudi Arabia
E? 39.838
5397.33132593	Distance in nautical miles
x<>y
60.420494571    Compass heading (30 degrees north of east)

This is counter-intuitive because, on a flat map of the world, Mecca appears far to the east and a little south of Boston. But if you find these two cities on a globe and connect them with a tight string, you can see that the shortest path goes north before it goes south.

Program

HP 35s users must read this!!

Distance output is in nautical miles. Change line D30 to 111.12 for kilometers, or 69.046767 for statute miles.

D01 LBL D
D02 DEG
D03 INPUT N
D04 STO X
D05 INPUT E
D06 INPUT N
D07 1
D08 θ,r→y,x
D09 INPUT E
D10 R↑
D11 -
D12 x<>y
D13 θ,r→y,x
D14 R↑
D15 x<>y
D16 y,x→θ,r
D17 x<>y
D18 RCL- X
D19 x<>y
D20 θ,r→y,x
D21 180
D22 R↓
D23 R↓
D24 +/-
D25 y,x→θ,r
D26 R↓
D27 -
D28 x<>y
D29 ACOS
D30 60
D31 ×
D32 RTN

HP-32SII: checksum = AAAA, length = 48.0
HP-33S:   checksum = EE88, length = 132
HP-35S:   checksum = EA58, length = 102