the difficulty to acquire a rank promotion for either. As with Elite, much of Frontier is concerned with trading: players can buy and sell a variety of goods—from food and computer parts to guns and slaves—with the aim of making the most profit possible from each trading run. Thus, learning to compare prices in various systems is essential for profitability, and calculating overheads for each trip (such as fuel, missiles, and hull repair) are essential skills. It often becomes apparent that a particular trading route is profitable, such as the Barnard's Star - Sol route. It is worth noting that some trade goods (particularly narcotics, nerve gas, weaponry and slaves) are illegal in many systems and attempting to trade in these can result in a fine from the police, which can often escalate into the police attacking you if not paid. However it is often worth the risk as illegal goods generally carry a very high price on the black market. Frontier substitutes Elite’s arcade flying style for one based rigidly on Newtonian physics: momentum must first be neutralised to bring the player's craft to a stop, and turning 180° has no effect on the direction of travel until previous momentum has been counteracted. The craft’s control is largely left to the player, but often day-to-day tasks such as navigating from a hyperspace exit-point to a desired planet or space-station and docking can be handed over to a ship's autopilot. Travel within a star system occurs across realistic distances at realistic speeds, and therefore even with the fastest ships capable of more than 10G of acceleration, intrasystem travel can take many hours. Therefore the game provides an "accelerate time" function that makes game time pass at 10, 100, 1000, or 10,000 times the normal rate. The issue of interstellar navigation is solved by the use of a hyperdrive to travel between stars. The player can select a system from the star map and "jump" to it, provided they are reasonably far from a settlement. They then arrive at the outskirts of that star system and must make their way to their destination. A ship's maximum range is calculated according to its mass, so small, light ships can have impressively large ranges. The time taken to travel the maximum range is always exactly one week, with shorter jumps taking less time. Unlike the rest of the game's travel, these jumps are