A creature generator is a type of actuator found in dungeon.dat. See Technical Documentation - File Formats - Dungeon File (DUNGEON.DAT).
Each creature type has a 'Base Health' value (BH). They are defined in graphics.dat for Atari ST versions.
Each level in the dungeon has a 'Level Experience Multiplier' value (LEM). They are defined in the dungeon.dat file.
Each creature generator has a 'Health Multiplier' value (HM). They are defined in the actuator properties in the dungeon.dat file.
When the game engine generates a creature, it uses the following formula to compute the creature's health value:
If HM = 0 Then the value is LEM * BH + Random(BH / 4 + 1)
If HM > 0 Then the value is HM * BH + Random(BH / 4 + 1)
Note: Random(x) is a function that returns a random number between 0 and x.