TI-BASIC, due to it's design, is compatable with almost all of the Ti-83+'s base commands (a base command is one that can be executed from the homescreen). This was designed mainly so you could use commands from the MATH menu for your program, but is also very helpful for using DRAW commands. The "Pxl-Test(" command is best used from a BASIC program, as are the Pxl-ON and Pxl-OFF commands. The difference between POINT and PIXEL commands is that POINT commands use X and Y values, while the PIXEL commands use the actual position on the screen. WHAT??? Okay, when you use POINT commands, the two arguments you give the command are X and Y values. This is affected by the ZOOM of your screen, because (1,3) in one zoom may be near the middle of the screen, but when you ZOOM IN it may be towards the edge. Also, if your ZOOM is set so that the point is not actually represented on the screen, it will draw it on the point that is closest. PIXEL commands, on the other hand, draw in the same place no matter what the ZOOM setting. The arguments for this command are rows down and columns right. PIXEL (0/0) would be at the very top left of the screen, while POINT (0,0) would be in the middle. I'm representing PIXEL values as (x/y) in this guide, so you don't get them mixed up with POINT commands. In a real-life situation, however, you would use a comma. Now that you have a basic understanding of the POINT and PIXEL syntax, lets continue on the the most important command you'll ever use in BASIC graphics programs, Pxl-Test. From the home screen, Pxl-test is used to check to see if there is a dark pixel on the Row/Column coordanetes you input. PIXEL commands are non-relative, so it dosen't matter what the point is from, Pxl-test will still count it the same. It returns a '1' if there is a pixel and a '0' if there is not. It can be used in IF-THEN-ELSE statements as well: prgmPIXEL Pxl-Test(1/1)->A If A=1 Then Disp "YES" Else Disp "NO" End If there is a PIXEL at (1/1), the program will display the text "YES". If there is not, it will display "NO". Pxl-test can be used in games as a "Hit detection" command. If you're building a SNAKE-style game, you would use Pxl-test to check to see if the player hits a wall. It can also be used in a more utilitarian way, to store a picture to a list, matrix, or string. The following program converts a picture into a list: prgmPICLIST ClrList LY \ ClrList LX \ ;These clear the lists to which you will be storing your picture. ClrHome DispGraph \ Pause \ Disp "PRESS ENTER TO \ Disp "BEGIN STORING \ ;Shows your picture and asks if you want to store it. Pause ClrHome Disp "WORKING... 1->F For(Y,0,62 \ For(X,0,94 \ ;Tests Left to Right, Top to Bottom. pxl-Test(Y,X)->P ;The omnipotent Pxl-test! If P=1 \ Then \ Y->LY(F \ X->LX(F \ ;If there is a pixel, it stores the coords to the lists LX and LY on row F F+1->F ;Moves down a row End ;End of IF-THEN End ;End of For(X... End ;End of For(Y... Output(8,1,"DONE! ;and its a wrap! A program to recall the picture would use Pxl-On to put on a point for every row in the lists. Now that you understand Pxl-test, go out and start programming! You will learn more tricks as you go! Thanks for reading John Hawk (Blueo)