Could you please review my IELTS Task 1?

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Topic: Could you please review my IELTS Task 1? I would really appreciate that.

My essay:

The chart compares the sales of the top five mobile phones manufacturers, Samsung, Apple, Nokia, LG and ZTE for three separate years, 2009, 2011 and 2013, representing each sales number using shades of bluish-green.

Overall, it appears that Samsung and Nokia are the brands that dominated the market, selling more units of the appliance than its adversaries. On the contrary, ZTE, however, lagged behind in the competition near the end of the period.

First of all, back in 2009, Nokia is considered to be the best-seller, selling just below 450 devices, which was reduced to about 420 in 2011 and to almost half of its original sales margin. On the other hand, Samsung observed a boost in its sales, from approximately 225, increasing by about 100 in 2011, it almost doubles in 2013.
With regards to the sales figures of Apple, it eventually grew six times its original number of 25, showing nearly 100 in 2011. However, for ZTE it started from 50 and reached about 60 rising to five units in 2011. Nevertheless, it dwindled for LG from 125 to about 90, then falls to 70.