# Gnuplot script to generate EMC plot, for Gnuplot version 4.2.
# Author: User hankwang on Wikipedia (2010).
# Equations taken from the Wikipedia article as of 2010-12-31.
# TF = temperature in deg F, TC = temp. in deg C

W(TF)  = 330   + 0.452*TF  + 0.00415*TF**2
k(TF)  = 0.791 + 4.63e-4*TF - 8.44e-7*TF**2
k1(TF) = 6.34  + 7.75e-4*TF - 9.35e-5*TF**2
k2(TF) = 1.09  + 2.84e-2*TF - 9.04e-5*TF**2

emcx(TF,k1,k2,kh)=1800./W(TF)  * (kh/(1-kh)  + (k1*kh+2*k1*k2*kh**2)/(1+k1*kh+k1*k2*kh**2))

emcF(TF,h)=emcx(TF,k1(TF),k2(TF),k(TF)*h)

C2F(TC)=TC*1.8+32
F2C(TF)=(TF-32)*5.0/9

emcC(TC,h)=emcF(C2F(TC),h)

set xlab 'Relative humidity (%)'
set xra [0:100]
set ylab 'EMC (%)'
set key top left

set term svg enhanced size 480,320
set outp 'emc.svg'

plot \
    emcC(0,x*0.01)   ti '0 ^oC (32 ^oF)' lt -1 lw 2, \
    emcC(30,x*0.01)  ti '30 ^oC (86 ^oF)' lt 3 lw 2, \
    emcC(60,x*0.01)  ti '60 ^oC (140 ^oF)' lt 2 lw 2, \
    emcC(120,x*0.01) ti '120 ^oC (248 ^oF)' lt 1 lw 2

set outp