In Version 1.40 of the Excel workbook, we’ve added a feature to allow you to control how the bet is submitted to the Exchange(s).
BACK-SP – means bet in the pre-race market, with a fall-back to the Starting Price if your bet is not matched before the market turns “in-play”
BACKSP – means take the Exchanges Starting Price only.
There is a more detailed explanation of this feature in the workbook itself.