Grade step start date per employee

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Hi, would anyone be able to point me in the right direction for creating a report that tells me how long each employee has been at their current grade step? We're looking to use this to identify employees reaching their grade step anniversary date, in order to apply pay progression. I'm struggling to find the right subject area in OTBI that gives an effective start date for grade step for each employee. I don't really want to fetch salary start dates, as it's feasible employees may have had salary changes due to e.g. hours changed since moving to their current