american tower corporation and subsidiaries notes to consolidated financial statements as of december 31 , 2010 , total unrecognized compensation expense related to unvested restricted stock units granted under the 2007 plan was $ 57.5 million and is expected to be recognized over a weighted average period of approximately two years . employee stock purchase plan 2014the company maintains an employee stock purchase plan ( 201cespp 201d ) for all eligible employees . under the espp , shares of the company 2019s common stock may be purchased during bi-annual offering periods at 85% ( 85 % ) of the lower of the fair market value on the first or the last day of each offering period . employees may purchase shares having a value not exceeding 15% ( 15 % ) of their gross compensation during an offering period and may not purchase more than $ 25000 worth of stock in a calendar year ( based on market values at the beginning of each offering period ) . the offering periods run from june 1 through november 30 and from december 1 through may 31 of each year . during the 2010 , 2009 and 2008 offering periods employees purchased 75354 , 77509 and 55764 shares , respectively , at weighted average prices per share of $ 34.16 , $ 23.91 and $ 30.08 , respectively . the fair value of the espp offerings is estimated on the offering period commencement date using a black-scholes pricing model with the expense recognized over the expected life , which is the six month offering period over which employees accumulate payroll deductions to purchase the company 2019s common stock . the weighted average fair value for the espp shares purchased during 2010 , 2009 and 2008 was $ 9.43 , $ 6.65 and $ 7.89 , respectively . at december 31 , 2010 , 8.7 million shares remain reserved for future issuance under the plan . key assumptions used to apply this pricing model for the years ended december 31 , are as follows: .

2010: range of risk-free interest rate: -0.22
weighted average risk-free interest rate: -0.22
expected life of shares: 6
range of expected volatility of underlying stock price: -35.26
weighted average expected volatility of underlying stock price: -35.26
expected annual dividends: n/a
2009: range of risk-free interest rate: -0.29
weighted average risk-free interest rate: -0.38
expected life of shares: 6
range of expected volatility of underlying stock price: -35.31
weighted average expected volatility of underlying stock price: -35.83
expected annual dividends: n/a
2008: range of risk-free interest rate: -1.99
weighted average risk-free interest rate: -2.58
expected life of shares: 6
range of expected volatility of underlying stock price: -27.85
weighted average expected volatility of underlying stock price: -28.51
expected annual dividends: n/a

13 . stockholders 2019 equity warrants 2014in august 2005 , the company completed its merger with spectrasite , inc . and assumed outstanding warrants to purchase shares of spectrasite , inc . common stock . as of the merger completion date , each warrant was exercisable for two shares of spectrasite , inc . common stock at an exercise price of $ 32 per warrant . upon completion of the merger , each warrant to purchase shares of spectrasite , inc . common stock automatically converted into a warrant to purchase shares of the company 2019s common stock , such that upon exercise of each warrant , the holder has a right to receive 3.575 shares of the company 2019s common stock in lieu of each share of spectrasite , inc . common stock that would have been receivable under each assumed warrant prior to the merger . upon completion of the company 2019s merger with spectrasite , inc. , these warrants were exercisable for approximately 6.8 million shares of common stock . of these warrants , warrants to purchase approximately none and 1.7 million shares of common stock remained outstanding as of december 31 , 2010 and 2009 , respectively . these warrants expired on february 10 , 2010 . stock repurchase program 2014during the year ended december 31 , 2010 , the company repurchased an aggregate of approximately 9.3 million shares of its common stock for an aggregate of $ 420.8 million , including commissions and fees , of which $ 418.6 million was paid in cash prior to december 31 , 2010 and $ 2.2 million was included in accounts payable and accrued expenses in the accompanying consolidated balance sheet as of december 31 , 2010 , pursuant to its publicly announced stock repurchase program , as described below. .

Questions:
what was the weighted average fair value for the espp shares in 2010?
and what was it in 2009?
what was, then, the change over the year?
how much does this change represent in relation to the weighted average fair value for the espp shares in 2009, in percentage?

Answers:
9.43
6.65
2.78
41.8%