Wombat Combat D Green Ashford, Kent. Can you guide the wombat down into the underground chambers of Deep Fort to destroy the Mad Master computer lurking there? I hope so. The fate of Western Civilisation rests on your 48K Spectrum. The game utilises an apparently unique method of regis- tering damage, as each one of the three main systems of the wombat has its own damage monitor and is affected by different hazards. Other potential dangers on your mission include the moderately brain-dead flying robot and boun- cing missiles, against which your most effective forms of defence are either running away or using your unbelievably short range tactical nuclear weapons, activated by key 0. Use the arrow keys to move, or change them in lines 160 and 170. Since the actual destruction of the master computer is not really all that hard, to get a reasonable score of over 2000 points you also need to collect all of the batteries that are lying around by some improbably coincidence. These batteries and various other objects have somehow been granted the power of levitation and hover in the air. The wombat is susceptible to falling if there is nothing to support it. The program is a good example of sound effects overkill, since hardly anything ever happens in total silence. The five mindless tunes embedded in the game are all done from Basic, but to show that the Spectrum can do more than beep, two machine-code routines are used. If you want to experi- ment with these, then have a look at line 2790, which sets up the variables to be used as follows: Poke lf, low (least significant) byte of frequency Poke hf, high (most significant) byte of frequency Poke len, number of beeps to be made Poke bep, length of each beep Then use Usr urun for a sound effect that goes up in pitch, or Usr drun for a sound effect which goes down in pitch. Be very careful when using numerically low frequen- cies, as if an uprunning sound effect goes into negative frequency values then a boring breakproof beep will occupy your computer for anything up to several hours. The amazingly efficient language of machine code is also used to detect user-defined graphics and to move the mis- siles. Note that all this machine code means that multiple saves before running are essential, as checksums can't find all your errors and just one poke can send all 16K of program to that great Ram chip in the sky.