The [Turn] modifier on engines gives +10% bonus to turn rate. The [+Turn] modifier on fleet engineering consoles gives approximately +20% bonus to turn rate (the exact percentage depends on mark). But this is misleading, because the console turn modifier actually gives more than twice the bonus of the engine turn modifier. The reason is that while the console turn modifier applies to the base turn rate (BTR) of the ship, the engine turn modifier applies to BTR - 3. The console turn modifier uses the new formula for RCS accelerators introduced in "Legacy of Romulus", but the engine turn modifier still uses the old formula from before "Legacy of Romulus".