We found that the EMA value of the finance chart is slightly changed during zoom in/out or drag the chart to left or right. It is no problem when EMA with smaller value (e.g. EMA 10, 20) but has problem on larger value (e.g. EMA 50). Do you have any idea? Thanks!
Thus to compute today's EMA, you must know yesterday's EMA. To computer yesterday's EMA, you must know the day before yesterday's EMA. This definition is an infinite recursion and is not possible to compute. We need to assume the EMA of a "starting date" to be the closing price itself, then we can start the computation from there onwards.
Because the starting date can depend on the zoom level, so the EMA can differ depending on the zoom level.
The inconsistency effect is less severe if the extra points is significantly larger than the EMA period. For example, if you have 50 days EMA, and you provide 100 extra points, although the EMA can still differ, it will be less than if only 30 extra points are used. It also explains why the effect is smaller for 10 or 20 days EMA.