interest rate derivatives . in connection with the issuance of floating rate debt in august and october 2008 , the company entered into three interest rate swap contracts , designated as cash flow hedges , for purposes of hedging against a change in interest payments due to fluctuations in the underlying benchmark rate . in december 2010 , the company approved a plan to refinance the term loan in january 2011 resulting in an $ 8.6 million loss on derivative instruments as a result of ineffectiveness on the associated interest rate swap contract . to mitigate counterparty credit risk , the interest rate swap contracts required collateralization by both counterparties for the swaps 2019 aggregate net fair value during their respective terms . collateral was maintained in the form of cash and adjusted on a daily basis . in february 2010 , the company entered into a forward starting interest rate swap contract , designated as a cash flow hedge , for purposes of hedging against a change in interest payments due to fluctuations in the underlying benchmark rate between the date of the swap and the forecasted issuance of fixed rate debt in march 2010 . the swap was highly effective . foreign currency derivatives . in connection with its purchase of bm&fbovespa stock in february 2008 , cme group purchased a put option to hedge against changes in the fair value of bm&fbovespa stock resulting from foreign currency rate fluctuations between the u.s . dollar and the brazilian real ( brl ) beyond the option 2019s exercise price . lehman brothers special financing inc . ( lbsf ) was the sole counterparty to this option contract . on september 15 , 2008 , lehman brothers holdings inc . ( lehman ) filed for protection under chapter 11 of the united states bankruptcy code . the bankruptcy filing of lehman was an event of default that gave the company the right to immediately terminate the put option agreement with lbsf . in march 2010 , the company recognized a $ 6.0 million gain on derivative instruments as a result of a settlement from the lehman bankruptcy proceedings . 21 . capital stock shares outstanding . the following table presents information regarding capital stock: .

Table:
( in thousands ) | december 31 , 2010 | december 31 , 2009
shares authorized | 1000000 | 1000000
class a common stock | 66847 | 66511
class b-1 common stock | 0.6 | 0.6
class b-2 common stock | 0.8 | 0.8
class b-3 common stock | 1.3 | 1.3
class b-4 common stock | 0.4 | 0.4
cme group has no shares of preferred stock issued and outstanding .
associated trading rights .
members of cme , cbot , nymex and comex own or lease trading rights which entitle them to access the trading floors , discounts on trading fees and the right to vote on certain exchange matters as provided for by the rules of the particular exchange and cme group 2019s or the subsidiaries 2019 organizational documents .
each class of cme group class b common stock is associated with a membership in a specific division for trading at cme .
a cme trading right is a separate asset that is not part of or evidenced by the associated share of class b common stock of cme group .
the class b common stock of cme group is intended only to ensure that the class b shareholders of cme group retain rights with respect to representation on the board of directors and approval rights with respect to the core rights described below .
trading rights at cbot are evidenced by class b memberships in cbot , at nymex by class a memberships in nymex and at comex by comex division memberships in comex .
members of the cbot , nymex and comex exchanges do not have any rights to elect members of the board of directors and are not entitled to receive dividends or other distributions on their memberships .
the company is , however , required to have at least 10 cbot directors ( as defined by its bylaws ) until its 2012 annual meeting. .

Question: what is the estimated percentual increase observed in the class a common stock during the years 2009 and 2010?
Answer: 0.5%
Calculation: divide(66847, 66511), subtract(#0, const_1)