Hi, I have been trading the S&P for about two years, and am developing ideas for FX trading. I have a few questions about data: 1. All of the data providers I've come across offer a) only bid, or b)bid and ask. In most cases the ask is derived from the bid as the spread is constant. No one seems to offer last trade. Is this because FX is not centralised around an exchange and so trade details cannot be known? 2. Given the limitations of bid only data with, for example Tradestation 7, is the best way to make back testing realsitic to add the spread to the slippage? e.g. $30 on EURUSD? Regards La di da