Sometimes slicer based calculation does not return the expected results.Any specific reason why?

I want to divide a total (10000) by average of Exchange rates for specifc quarter (6.78232). I have created Dynamic measure based on quarters to calculate average of Exchnage Rates. When I use the Dynamic slicer results in Card Visual it shows perfect Average number that I am expecting e.g. 6.78232, however as soon as I use the same Dynamic Measure in DAX as a divisor results are different. Minor difference though however I need exact results. Any logical or techincal flaw you guys can see  here, any suggestions?