Not much, just for the record. Here's a short and sweet program to calculate the gain or loss of your ELO rating.

Just do:

K-value

ENTER

Opponent's ELO rating

ENTER

Your ELO rating

ENTER

Score (1 = you win, 0.5 = draw, 0 = you lose)

XEQ"ELO"

The result is how much you gain or lose in ELO rating.

The program:

001 LBL"ELO"

002 "K^O^Y^W,D,L"

003 RDN

004 -

005 400

006 /

007 10

008 X<>Y

009 Y^X

010 1

011 +

012 1/X

013 CHS

014 RCL Z

015 +

016 *

017 END

Line 002 is included purely as a reminder of how to use the program (the sequence of values entered).