note 18 2013 earnings per share ( eps ) basic eps is calculated by dividing net earnings attributable to allegion plc by the weighted-average number of ordinary shares outstanding for the applicable period . diluted eps is calculated after adjusting the denominator of the basic eps calculation for the effect of all potentially dilutive ordinary shares , which in the company 2019s case , includes shares issuable under share-based compensation plans . the following table summarizes the weighted-average number of ordinary shares outstanding for basic and diluted earnings per share calculations. .

Table: in millions 2017 2016 2015 weighted-average number of basic shares 95.1 95.8 95.9 shares issuable under incentive stock plans 0.9 1.1 1.0 weighted-average number of diluted shares 96.0 96.9 96.9

at december 31 , 2017 , 0.1 million stock options were excluded from the computation of weighted average diluted shares outstanding because the effect of including these shares would have been anti-dilutive . note 19 2013 commitments and contingencies the company is involved in various litigations , claims and administrative proceedings , including those related to environmental and product warranty matters . amounts recorded for identified contingent liabilities are estimates , which are reviewed periodically and adjusted to reflect additional information when it becomes available . subject to the uncertainties inherent in estimating future costs for contingent liabilities , except as expressly set forth in this note , management believes that any liability which may result from these legal matters would not have a material adverse effect on the financial condition , results of operations , liquidity or cash flows of the company . environmental matters the company is dedicated to an environmental program to reduce the utilization and generation of hazardous materials during the manufacturing process and to remediate identified environmental concerns . as to the latter , the company is currently engaged in site investigations and remediation activities to address environmental cleanup from past operations at current and former production facilities . the company regularly evaluates its remediation programs and considers alternative remediation methods that are in addition to , or in replacement of , those currently utilized by the company based upon enhanced technology and regulatory changes . changes to the company's remediation programs may result in increased expenses and increased environmental reserves . the company is sometimes a party to environmental lawsuits and claims and has received notices of potential violations of environmental laws and regulations from the u.s . environmental protection agency and similar state authorities . it has also been identified as a potentially responsible party ( "prp" ) for cleanup costs associated with off-site waste disposal at federal superfund and state remediation sites . for all such sites , there are other prps and , in most instances , the company 2019s involvement is minimal . in estimating its liability , the company has assumed it will not bear the entire cost of remediation of any site to the exclusion of other prps who may be jointly and severally liable . the ability of other prps to participate has been taken into account , based on our understanding of the parties 2019 financial condition and probable contributions on a per site basis . additional lawsuits and claims involving environmental matters are likely to arise from time to time in the future . the company incurred $ 3.2 million , $ 23.3 million , and $ 4.4 million of expenses during the years ended december 31 , 2017 , 2016 and 2015 , respectively , for environmental remediation at sites presently or formerly owned or leased by the company . in the fourth-quarter of 2016 , with the collaboration and approval of state regulators , the company launched a proactive , alternative approach to remediate two sites in the united states . this approach will allow the company to more aggressively address environmental conditions at these sites and reduce the impact of potential changes in regulatory requirements . as a result , the company recorded a $ 15 million charge for environmental remediation in the fourth quarter of 2016 . environmental remediation costs are recorded in costs of goods sold within the consolidated statements of comprehensive income . as of december 31 , 2017 and 2016 , the company has recorded reserves for environmental matters of $ 28.9 million and $ 30.6 million . the total reserve at december 31 , 2017 and 2016 included $ 8.9 million and $ 9.6 million related to remediation of sites previously disposed by the company . environmental reserves are classified as accrued expenses and other current liabilities or other noncurrent liabilities based on their expected term . the company's total current environmental reserve at december 31 , 2017 and 2016 was $ 12.6 million and $ 6.1 million and the remainder is classified as noncurrent . given the evolving nature of environmental laws , regulations and technology , the ultimate cost of future compliance is uncertain. .

Question: considering the years 2015-2017 , what is the average expense for environmental remediation at sites , in millions of dollars?
Answer: 10.3
Calculation: divide(add(4.4, add(3.2, 23.3)), const_3)
Explanation: it is the sum of all environmental remediation expenses during these years , divided by three ( number of years ) .