ÓUNDIAL 128
ÂY ÍARK ÊORDAN

ÏNE EVENING RECENTLY É WAS SITTING IN MY LIVING ROOM WITH THE ÔÖ ON AND THE LIGHTS OFF. É WAS VACANTLY WATCHING A SHADOW ON THE CEILING WHEN IT STRUCK ME THAT THE LIGHT FROM THE ÔÖ HAD ENOUGH POWER TO CREATE MOVING SHADOWS THAT CHANGED AS IMAGES MOVED ON THE SCREEN. ÉT DAWNED ON ME THAT THE ÔÖ WAS A LIGHT SOURCE, ACTUALLY A BUNCH OF LIGHTS, CALLED PIXELS (FOR "PICTURE ELEMENTS").

ÈMMM. ÈOW COULD THIS BE DEMONSTRATED WITH MY COMPUTER? É DID SOME QUICK-AND-DIRTY PROGRAMMING TO MOVE A WHITE SPRITE ACROSS A DARK SCREEN, AND SURE ENOUGH, A PENCIL PROPPED AGAINST THE SCREEN CREATED A MOVING SHADOW.É THEN REMEMBERED HOW MY KIDS HAD SPOTTED A SUNDIAL RECENTLY, AND ASKED HOW IT WORKED. ÈERE WAS A CHANCE TO KILL TWO BIRDS WITH ONE STONE.

"ÓUNDIAL 128," IS THE "LAB REPORT." ÓCROUNGE AROUND YOUR HOUSE AND FIND A PIECE OF CARDBOARD ABOUT A FOOT SQUARE, A NAIL AT LEAST THREE INCHES LONG AND A PENCIL. ÊAB THE NAIL THROUGH THE CARDBOARD NEAR THE CENTER. ÔHIS NAIL IS THE GNOMON (THE PART THAT CASTS THE SHADOW) ON YOUR SUNDIAL. ÔHE CARDBOARD IS THE DIAL'S FACE. ÐLACE THE CARDBOARD JUST UNDER THE FRONT OF YOUR MONITOR WITH THE NAIL CENTERED WITH THE SCREEN. ÒUN THE PROGRAM AND DARKEN THE ROOM.

ÙOU HAVE THREE OPTIONS: ÓET, ÇUESS AND ÅLSE. ÐRESS Ó TO SET YOUR TIMEPIECE, AND YOU'LL SEE THE MORNING SUN (A WHITE BALL) RISE IN THE EAST (THE LEFT SIDE OF YOUR SCREEN). ÔHE TIME OF DAY WILL BE DISPLAYED ALONG WITH IT: 5:30, 5:35, AND SO ON UP TO 6 A.M. ÔHEN EVERYTHING WILL FREEZE TO LET YOU MAKE YOUR FIRST MARKING.

ÌOOK DOWN AT YOUR SUNDIAL. ÙOU'LL SEE THAT THE STANDING POINTER DOES INDEED CAST A SHADOW, NOT SHARP, BUT VISIBLE. ÔRACE THE SHADOW-LINE WITH A PENCIL. ÈIT ANY KEY TO MOVE THE SUN ALONG BY HOUR, TRACING THE SHADOW AS IT MOVES UNTIL YOU HAVE A COMPLETE, CALIBRATED SUNDIAL (6 A.M. TO 7 P.M.). ×HENEVER YOU RUN THE PROGRAM, YOU'LL NEED TO RECALIBRATE BY MOVING THE CARDBOARD UNTIL YOU GET THE LINES TO MATCH UP WITH THE TIMES.

×HEN YOU SELECT ÇUESS, THE SUN WILL AGAIN MAKE ITS ASCENT, ONLY IT WILL STOP ALONG THE WAY AND YOU WILL BE ASKED TO GUESS THE TIME USING THE CURSOR KEYS, WHICH STEP THROUGH HOURS AND MINUTES IN FIVE-MINUTE INCREMENTS. ÍAKE YOUR SELECTION AND PRESS ÒETURN TO SEE THE RESULTS. ÔHE THIRD OPTION IS JUST FOR THE HECK OF IT, AND LETS YOU WATCH THE SUN RISE AND FALL WITH THE TIME DISPLAYED ALONG WITH IT.ÄOING THIS LITTLE EXPERIMENT PROMPTED ME TO THINK OF OTHER PROJECTS THAT USE THE MONITOR AS A LIGHT SOURCE: AN ANIMATED SHADOW SHOW OR A GAME THAT SENDS LIGHT BEAMS TO A MAP TO GIVE CLUES.

ÈAVE YOU DONE A NIFTY HOME EXPERIMENT WITH YOUR ÃOMMODORE 128? ÓEND ME A DESCRIPTION OF IT, INCLUDING YOUR NAME, ADDRESS AND TELEPHONE NUMBER TO THE ÒÕÎ EDITORS USING ÔHE ÌETTERS ÔO THE ÅDITOR OPTION ON THIS ÒEÒÕÎ DISK. ÉF THEY GET ENOUGH RESPONSES É'LL DEVOTE AN UPCOMING 128 ÍODE COLUMN TO THEM.