research and development we are committed to investing in highly productive research and development capabilities , particularly in electro-mechanical systems . our research and development ( "r&d" ) expenditures were approximately $ 48.3 million , $ 47.3 million and $ 45.2 million for the years ended december 31 , 2017 , 2016 and 2015 , respectively . we concentrate on developing technology innovations that will deliver growth through the introduction of new products and solutions , and also on driving continuous improvements in product cost , quality , safety and sustainability . we manage our r&d team as a global group with an emphasis on a global collaborative approach to identify and develop new technologies and worldwide product platforms . we are organized on a regional basis to leverage expertise in local standards and configurations . in addition to regional engineering centers in each geographic region , we also operate a global engineering center of excellence in bangalore , india . seasonality our business experiences seasonality that varies by product line . because more construction and do-it-yourself projects occur during the second and third calendar quarters of each year in the northern hemisphere , our security product sales , typically , are higher in those quarters than in the first and fourth calendar quarters . however , our interflex business typically experiences higher sales in the fourth calendar quarter due to project timing . revenue by quarter for the years ended december 31 , 2017 , 2016 and 2015 are as follows: .
considering the years 2016-2017 , what is the average value recorded for reserves for environmental matters , in millions of dollars?
employees we currently have approximately 10000 employees . environmental regulation we have a dedicated environmental program that is designed to reduce the utilization and generation of hazardous materials during the manufacturing process as well as to remediate identified environmental concerns . as to the latter , we are 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 . we are sometimes a party to environmental lawsuits and claims and have received notices of potential violations of environmental laws and regulations from the u.s . environmental protection agency ( the "epa" ) and similar state authorities . we have 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 , our involvement is minimal . in estimating our liability , we have assumed that we 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 . we 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 us . as of december 31 , 2017 and 2016 , we have recorded reserves for environmental matters of $ 28.9 million and $ 30.6 million . of these amounts $ 8.9 million and $ 9.6 million , respectively , relate to remediation of sites previously disposed by us . given the evolving nature of environmental laws , regulations and technology , the ultimate cost of future compliance is uncertain. .