Please answer the given financial question based on the context.
Context: american tower corporation and subsidiaries notes to consolidated financial statements 2014 ( continued ) pro forma disclosure 2014the company has adopted the disclosure-only provisions of sfas no . 123 , as amended by sfas no . 148 , and has presented such disclosure in note 1 . the 201cfair value 201d of each option grant is estimated on the date of grant using the black-scholes option pricing model . the weighted average fair values of the company 2019s options granted during 2004 , 2003 and 2002 were $ 7.05 , $ 6.32 , and $ 2.23 per share , respectively . key assumptions used to apply this pricing model are as follows: .
||2004|2003|2002|
|approximate risk-free interest rate|4.23% ( 4.23 % )|4.00% ( 4.00 % )|4.53% ( 4.53 % )|
|expected life of option grants|4 years|4 years|5 years|
|expected volatility of underlying stock ( the company plan )|80.6% ( 80.6 % )|86.6% ( 86.6 % )|92.3% ( 92.3 % )|
|expected volatility of underlying stock ( atc mexico and atc south america plans )|n/a|n/a|n/a|
|expected dividends|n/a|n/a|n/a|
voluntary option exchanges 2014in february 2004 , the company issued to eligible employees 1032717 options with an exercise price of $ 11.19 per share , the fair market value of the class a common stock on the date of grant . these options were issued in connection with a voluntary option exchange program entered into by the company in august 2003 , where the company accepted for surrender and cancelled options ( having an exercise price of $ 10.25 or greater ) to purchase 1831981 shares of its class a common stock . the program , which was offered to both full and part-time employees , excluding the company 2019s executive officers and its directors , called for the grant ( at least six months and one day from the surrender date to employees still employed on that date ) of new options exercisable for two shares of class a common stock for every three shares of class a common stock issuable upon exercise of a surrendered option . no options were granted to any employees who participated in the exchange offer between the cancellation date and the new grant date . in may 2002 , the company issued to eligible employees 2027612 options with an exercise price of $ 3.84 per share , the fair market value of the class a common stock on the date of grant . these options were issued in connection with a voluntary option exchange program entered into by the company in october 2001 , where the company accepted for surrender and cancelled options to purchase 3471211 shares of its class a common stock . the program , which was offered to both full and part-time employees , excluding most of the company 2019s executive officers , called for the grant ( at least six months and one day from the surrender date to employees still employed on that date ) of new options exercisable for two shares of class a common stock for every three shares of class a common stock issuable upon exercise of a surrendered option . no options were granted to any employees who participated in the exchange offer between the cancellation date and the new grant date . atc mexico holding stock option plan 2014the company maintains a stock option plan in its atc mexico subsidiary ( atc mexico plan ) . the atc mexico plan provides for the issuance of options to officers , employees , directors and consultants of atc mexico . the atc mexico plan limits the number of shares of common stock which may be granted to an aggregate of 360 shares , subject to adjustment based on changes in atc mexico 2019s capital structure . during 2002 , atc mexico granted options to purchase 318 shares of atc mexico common stock to officers and employees . such options were issued at one time with an exercise price of $ 10000 per share . the exercise price per share was at fair market value as determined by the board of directors with the assistance of an independent appraisal performed at the company 2019s request . the fair value of atc mexico plan options granted during 2002 were $ 3611 per share as determined by using the black-scholes option pricing model . as described in note 10 , all outstanding options were exercised in march 2004 . no options under the atc mexico plan were granted in 2004 or 2003 , or exercised or cancelled in 2003 or 2002 , and no options were exercisable as of december 31 , 2003 or 2002 . ( see note 10. ) .
Question: based on the black-scholes option pricing model what was the percent of the change in approximate risk-free interest rate from 2003 to 2004
Answer:
0.0575