What you do is use the UP arrow to change your BASE to match any number, or INVADER, that is advancing towards you. Once you change your Base to that Invader number you press the DOWN arrow to destroy the Invader.

If you destroy 2 or more Invaders in a row that add up to 10, 20, 30 etc then you get a 'n', or Mother Ship, advancing towards you which you can then destroy for 150 points.

The closer the the right hand side of the screen the Invaders are when you destroy them the more points you get for each, eg. 80 points for an Invader in the first position on the right, then less 10 points each position closer to your Base (ie. 70, 60, 50, 40, 30, 20, 10.)

You have 3 lives which are displayed next to you by 3 lines next to your Base.

The game has 9 levels and each level the Invaders advance faster towards you. Once you get past the 9th level it goes back to level 1. It's pretty hard to get through the 7th, 8th or 9th levels though so it can take a while to do this.

• UP arrow - Aim
• DOWN arrow - fire
• X button - start game