Principal market means the single securities market with the largest aggregate reported trading volume for the class of securities during the 12 full calendar months immediately preceding the filing of the registration statement; or, if there is no registration statement or if the distribution involves the sale of securities on a delayed basis pursuant to 230.415 of this chapter, during the 12 full calendar months immediately preceding the determination of the offering price. For the purpose of determining the aggregate trading volume in a security, the trading volume of depositary shares representing such security shall be included, and shall be multiplied by the multiple or fraction of the security represented by the depositary share. For purposes of this paragraph, depositary share means a security, evidenced by a depositary receipt, that represents another security, or a multiple or fraction thereof, deposited with a depositary.
17 CFR § 242.100
Preliminary note: Any transaction or series of transactions, whether or not effected pursuant to the provisions of Regulation M ( 242.100-242.105 of this chapter), remain subject to the antifraud and antimanipulation provisions of the securities laws, including, without limitation, Section 17(a) of the Securities Act of 1933 [15 U.S.C. 77q(a)] and Sections 9, 10(b), and 15(c) of the Securities Exchange Act of 1934 [15 U.S.C. 78i, 78j(b), and 78o(c)].