okay
Old rule
nadex took last 25 non-sequential mid quotes (meaning if a quote was the same mutliple times in a row it was not included) then averaged the middle 15 prices.
New rule
Nadex takes the last 25 mid quotes (meaning if they are the same they still count making it more sensitive) - then average the middle 15 prices
Buying and selling has nothing to do with it at this point.
Note it is MID quote of reuters data feed (expensive) Your looking at FXCM or other data feed and looking at last quote. So there can be a bit of a difference so maybe a couple ticks. You will be able to tell just by looking at it.
So either no adjustment is necessary or you can look to see if one is off by a couple ticks etc… the number one rule here is just be consistent and the averages will end up the same.
Dont make it complex.