10  COM I,A[37,61],B,E[3],P,P4,A$[10],D[19,2],R1
20  REM PROGRAM NAME = ORB2, PLOTS ORBITS FOR KEP1, KEP2, ORBECC
30  REM JEFFERSON COUNTY WRITING TEAM, LAKEWOOD, COLORADO
40  REM 9 AUGUST 1973
50  GOTO 80
60  CHAIN "$KEP1"
70  CHAIN "$KEP2"
80  DIM V[72],B$[20]
90  Z=240
100  PRINT 
110  PRINT "----- PLOT OF ORBIT(S):"
120  PRINT 
130  FOR Z=I TO 37
140  N=I-I
150  FOR W=I TO 61
160  IF A[Z,W] THEN 200
170  NEXT W
180  IF  NOT N THEN 350
190  GOTO 230
200  N=N+I
210  V[N]=W
220  GOTO 170
230  FOR P=I TO N
240  W=V[P]
250  IF A[Z,W]=I THEN 280
260  IF A[Z,W]=2 THEN 300
270  GOTO 320
280  E$="*"
290  GOTO 330
300  E$="."
310  GOTO 330
320  E$="@"
330  PRINT TAB(V[P]-I);E$;
340  NEXT P
350  PRINT 
360  NEXT Z
370  GOTO P4+I OF 380,580,610
380  PRINT "DO YOU WANT TO RUN THIS PROGRAM AGAIN?  ";
390  ENTER Z,D,B$
400  PRINT '13
410  IF B$="YES" THEN 520
420  IF B$#"NO" THEN 380
430  PRINT "DO YOU KNOW HOW TO CALCULATE THE ECCENTRICITY OF AN ORBIT?  ";
440  ENTER Z,D,B$
450  PRINT '13
460  IF B$="YES" THEN 540
470  IF B$#"NO" THEN 430
480  PRINT "TO LEARN HOW, REFER TO THE WORKSHEET FOR KEP1, OR TO"
490  PRINT "SECTION 6-2 OF THE BOOK,"
500  GOSUB 640
510  END 
520  A$="2"
530  GOTO 60
540  PRINT "THE PROGRAM ORBECC, DISCUSSED IN SECTION 6-3 OF THE BOOK,"
550  GOSUB 640
560  PRINT "PLOTS ORBITS FOR WHICH YOU CAN CALCULATE THE ECCENTRICITY."
570  END 
580  PRINT "USING THIS PLOTTED ORBIT, 1) LOCATE THE FOCI, AND"
590  PRINT "2) CALCULATE THE ECCENTRICITY."
600  END 
610  A$="3"
620  GOTO 70
630  END 
640  PRINT "   INTERACTIVE METHODS FOR TEACHING SELECTED TOPICS"
650  PRINT "   IN HIGH SCHOOL PHYSICS AND MATHEMATICS USING A COMPUTER"
660  RETURN 
670  END 
