Superb bit of space gaming usefulness. Makes adding the realism of fuel/remass usage to most 'build your own' games (or pre-designed, if you want to make more judgement calls). Three settings of fuel usage for speedy tactical (Full Thrust), slower tactical (Starmada), or slowest 'operational' (Triplanetary). Efficiency options give you plenty of wiggle room for tech levels within each 'setting'. It's one of those things that make me slap my forehead and say, 'Of course!' If you've any interest in even vagely realistic space gaming, this is worth every penny (and I'm usually hard on the more expensive per page PDFs, so).