changes will not be accepted since 0 is an invalid line number. Such code is typically created by first creating a line with a valid number, and then modifying the number field in the BASIC program area using direct memory manipulation, such as POKE. No copy protection is embedded into the game; moreover, the magnetic tapes of the time being unreliable, one could reuse the save entry point in the BASIC code (that was used by the original developers to have the game auto-run upon being loaded by the user) in order to save another program copy to the tape (for archival and backup purposes). The game is controlled by three of the keyboard cursor control keys (left, forward and right, respectively 5, 7 and 8 on the ZX81 keyboard). The game speed can also be controlled according to the original cassette inlay, the BASIC line 370 has a hardwired constant determining a busy waiting loop delay. The constant initially is set to 5; by varying it from 0 to 9 the game can be adjusted from faster to slower tempo. The 6 frame per second figure corresponds to the delay set to zero, while holding the "forward" key to run straight. A somewhat jerky motion is perceived at this slow framerate which gives a feeling of being jerked along with each step of a desperate heavy run. Development 3D Monster Maze was the first game programmed by Malcolm Evans based on a design by J.K.Greye. He worked in the aerospace industry, first in aircraft design, and then as a microprocessor scientist at Sperry Gyroscope in Bristol, United Kingdom. He received a ZX81 from his wife for his thirty-seventh birthday in April 1981. Malcolm developed basic aspects of the game to test what the computer was capable of, and completed it after adding design features suggested by J.K.Greye, including adding the T.Rex and turning the Maze into a game. Friends persuaded Malcolm that the game was of high enough quality to sell and it was eventually released by J.K. Greye Software in late 1981. When soon after that the Bristol branch of Sperry Gyroscope closed, Malcolm made a decision to concentrate fully on computer gaming. The firm New Generation Software he had founded kept producing 3D games for the Sinclair Research computers, and became synonymous with 3D gaming on this platform for some time. Some of his games were hailed