10 REM IBM PC
20 REM ENVUSE: ENVIRONMENTAL USE
30 CLS
40 SCREEN 1, 0: COLOR 15, 0
50 LINE (0, 0)-(319, 180), 3, B
60 LINE (0, 90)-(319, 90), 1
70 REM Coefficients
80 K0 = 9
90 K1 = .5
100 K2 = .05
110 K3 = .6
120 K4 = 15
130 K5 = .8
140 K6 = .06
150 K7 = .6
160 K8 = 0
170 K9 = .1
180 L1 = .4
190 L2 = 2
200 REM SCALING
210 DT = .1
220 T0 = 10: REM 32 year horizontal axis
230 Q0 = 66.7
240 A0 = 20
250 M0 = 10
260 D0 = 10
270 REM OUTSIDE SOURCES
280 IT = .1
290 JL = .3
300 PI = 10
310 PE = 1
320 I = 1
330 REM STARTING CONDITIONS
340 Q = 1
350 M = .1
360 A = .2
370 D = 0
380 Z = 1
390 REM EQUATIONS
400 R = I / (1 + K0)
410 PE = (L1 + Q) / (L2 * Q)
420 IF PE > 3 THEN PE = 3
430 REM CHANGE EQUATIONS
440 IF D = 0 THEN Z = 0
450 IF D > 0 THEN Z = 1
460 DQ = K1 * R - K2 * Q - K3 * Q * A
470 DA = K5 * M / PI - K6 * A - K7 * Q * A
480 DM = PE * K4 * A * Q + JL - K5 * M - IT * D - Z * K9 * M
490 DD = JL - Z * K9 * M
500 A = A + DA * DT
510 IF A < 0 THEN A = 0
520 Q = Q + DQ * DT
530 IF Q < 0 THEN Q = 1E-10
540 M = M + DM * DT
550 IF M < 0 THEN M = 0
560 D = D + DD * DT
570 IF D < 0 THEN D = 0
580 REM PLOTTING GRAPHS WITH TIME
590  PSET (T * T0, 180 - Q * Q0), 1
600  PSET (T * T0, 180 - (A * A0)), 2
610  PSET (T * T0, 90 - M * M0), 3
620  PSET (T * T0, 90 - D * D0), 1
630 T = T + DT
640  IF T * T0 < 319 GOTO 390
650  LOCATE 2, 2: PRINT "Envuse.bas": SLEEP: SLEEP
660 END