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: 5.8%