What is this method for seasonal adjustment calculation?

I got an example calculation for multiplicative model, which is shown as follows:

Quarter           1         2        3       4
Average         0.866    1.0005   1.403    0.660
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Seasonal factor  0.884    1.018   1.421    0.678


Then there is a note below:

Sum of averages = 3.9295. These should sum to 4, 4-3.9295=0.0705. Adding 0.0705/4=0.0176 to each average, to obtain the seasonal factors.

I saw from other resources that they are using "seasonal index" instead of "seasonal factor" by normalizing the values. Besides that, they also mentioned about X11, X12, ARIMA, and so on. I would like to know is, based on the example above, what is the method called?

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X11 is an older method of seasonally adjusting data. Here's a link:

http://www.census.gov/srd/www/sapaper/historicpapers.html

0.884 = 0.866 + 0.0176