Read the following texts and table with financial data from an S&P 500 earnings report carefully.Based on the question-answer history (if provided), answer the last question. The answer may require mathematical calculation based on the data provided.


note 4 : property , plant and equipment the following table summarizes the major classes of property , plant and equipment by category as of december 31 : 2015 2014 range of remaining useful weighted average useful life utility plant : land and other non-depreciable assets . . . . . . . . . . $ 141 $ 137 sources of supply . . . . . . . . . . . . . . . . . . . . . . . . . . 705 681 12 to 127 years 51 years treatment and pumping facilities . . . . . . . . . . . . . . 3070 2969 3 to 101 years 39 years transmission and distribution facilities . . . . . . . . . 8516 7963 9 to 156 years 83 years services , meters and fire hydrants . . . . . . . . . . . . . 3250 3062 8 to 93 years 35 years general structures and equipment . . . . . . . . . . . . . 1227 1096 1 to 154 years 39 years waste treatment , pumping and disposal . . . . . . . . . 313 281 2 to 115 years 46 years waste collection . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 399 5 to 109 years 56 years construction work in progress . . . . . . . . . . . . . . . . 404 303 total utility plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18099 16891 nonutility property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 378 3 to 50 years 6 years total property , plant and equipment . . . . . . . . . . . . . . . $ 18504 $ 17269 property , plant and equipment depreciation expense amounted to $ 405 , $ 392 , and $ 374 for the years ended december 31 , 2015 , 2014 and 2013 , respectively and was included in depreciation and amortization expense in the accompanying consolidated statements of operations . the provision for depreciation expressed as a percentage of the aggregate average depreciable asset balances was 3.13% ( 3.13 % ) for the year ended december 31 , 2015 and 3.20% ( 3.20 % ) for years december 31 , 2014 and 2013 . note 5 : allowance for uncollectible accounts the following table summarizes the changes in the company 2019s allowances for uncollectible accounts for the years ended december 31: . <table class='wikitable'><tr><td>1</td><td>-</td><td>2015</td><td>2014</td><td>2013</td></tr><tr><td>2</td><td>balance as of january 1</td><td>$ -35 ( 35 )</td><td>$ -34 ( 34 )</td><td>$ -27 ( 27 )</td></tr><tr><td>3</td><td>amounts charged to expense</td><td>-32 ( 32 )</td><td>-37 ( 37 )</td><td>-27 ( 27 )</td></tr><tr><td>4</td><td>amounts written off</td><td>38</td><td>43</td><td>24</td></tr><tr><td>5</td><td>recoveries of amounts written off</td><td>-10 ( 10 )</td><td>-7 ( 7 )</td><td>-4 ( 4 )</td></tr><tr><td>6</td><td>balance as of december 31</td><td>$ -39 ( 39 )</td><td>$ -35 ( 35 )</td><td>$ -34 ( 34 )</td></tr></table> .
Question: in 2013, as part of the company's noncollectable amounts, how much did those amounts written off represent in relation to the recovered ones?
Answer: 6.14286
Question: and from that year to 2015, what was the increase in the property, plant and equipment depreciation expense?
Answer: 31.0
Question: what is this increase as a portion of that depreciation expense in 2013?

0.08289