Use of formulas: annual interest securities. I am writing in response to your letter of June 1, 1983 regarding the appropriate method of calculating yield and dollar price on periodic-interest municipal securities which pay interest on an annual, rather than the more customary semi-annual, basis. You note in your letter that Board rule G-33 requires the use for purposes of computations of yield and dollar price on such securities of a formula which presumes semi-annual payment of interest (i.e., that formula set forth in subparagraph (b)(i)(B)(2) of the rule). You suggest that the rule should be amended to require the use of a formula that recognizes the annual interest payment cycle on the securities.

As I indicated to you in our previous telephone conversation on this subject, the industry has traditionally disregarded the unusual nature of the interest payment cycle on these securities when computing yields and dollar prices on them, and has followed the practice of using the standard formula for computing yield and dollar price on a security paying interest on a semi-annual basis for these purposes. As a result of this traditional practice, all of the calculators presently available for use by industry members when computing yields and dollar prices have been designed in accordance with the assumption that all periodic-interest municipal securities pay interest on a semi-annual basis; these calculator models cannot be used to compute yields and dollar prices on such securities on any other basis. Therefore, the adoption of a requirement that yields and dollar prices on securities which pay interest on an annual basis be computed by means of a formula which recognizes the annual nature of the interest payment cycle, such as you suggest, would render all of the existing calculator models obsolete, and require that all industry members incur the cost of purchasing new calculator equipment capable of performing such computations (equipment which does not, to my knowledge, exist as of yet).

It is because of the substantial compliance expense that would have been imposed on the industry that the Board declined to adopt a requirement such as you suggest at the time rule G-33 was promulgated, even though it recognized that the requirement that was adopted mandated the use of a formula that would produce slightly less accurate results. MSRB interpretation of June 6, 1983.