Type: Decimal

Return the price at fixed intervals at the start of the event. The available intervals [min] are 1, 2, 3, 4, 5, 10, 15, 30, 60, 120, 180.
If the price is not yet present, the variable returns null.

dbo.fn_PercDiff(@best_back_price, isnull(@price_2, @best_back_price))

returns the difference in tips between the current best back price and the price at two minutes at the start. If the price is not yet present (Null), it is converted to the same value of the best back price, producing a difference of zero ticks.