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Google Finance: Input Parameters For Simple Moving Averages
The difference is that for the one year time frame the data is represented based on daily data and the SMA is 20 days, whilst for the 5 year timeframe the data is automatically represented as weekly data with the SMA represented by 20 weeks not 20 days anymore. This happens due to daily data on this chart being too much data to represent over a 5 year period so the data defaults to weekly data over such a long period. If the chart is represented as weekly data then any indicators will also have to be represented in weekly data. If you use a more sophisticated charting program you can actually select to see daily or weekly data over longer periods such as 5 years or more.