Interpretation ID: 18432.drn

Mr. Andreas Geis
Bosch
Abteilung/Dept.: K4-RS/EWR5
FAX: GERMANY 7223/82/2310
FAX: (011) (49) 7223/82/2320

Dear Mr. Geis:

This responds to your request for an interpretation of metric conversions to Standard No. 104, Windshield Wiping and Washing Systems. You wish to know whether the measurement of 625 millimeters (mm) specified in the definition of "Glazing surface reference line" at S3, 571.104, in Title 49 of the Code of Federal Regulations is a typographical error. You state that depending on whether a conversion factor of 25 or 25.4 mm to the inch is used, the metric measurement could be 625 or 635 mm. You state that "10 mm would mean a considerable difference to the position of areas A, B, and C on the windshield."

As explained below, in part because of your letter, the National Highway Traffic Safety Administration (NHTSA) has amended the measurement in the definition of "Glazing surface reference line" to 635 mm. We agree that the 10 mm difference between 625 mm and 635 mm could result in a substantive change to Standard No. 104, a result that the agency did not intend when it converted English measurements to metric measurements.

In changing the Federal motor vehicle safety standards to metric measurements, NHTSA made a policy determination that, in order to arrive at measurements that would be easiest to work with, it would generally use equivalent conversions, not exact conversions. To illustrate, in converting an inch, the equivalent measurement in the metric system would be 2.5 centimeters, while the exact conversion would be 2.54 centimeters. (See Federal Register notice of April 21, 1992 (57 FR 14691).) The agency also did not intend to make any changes in the stringency of the affected safety standards.

In accordance with regulatory procedures, before the Standard No. 104 metric conversion measurements were made final, NHTSA gave the public an opportunity to comment on the proposed changes. In a Federal Register notice of March 15, 1994 (59 FR 11962), NHTSA proposed that the 25 inches specified in "Glazing surface reference line" be converted to 625 mm. NHTSA did so in accordance with its stated policy that it would generally use equivalent conversions, not exact conversions. Thus, in making the conversion, it multiplied 25 inches by 25 mm, not 25.4 mm.

Upon receiving your letter, NHTSA reexamined the conversion of the measurement in "Glazing surface reference line." It was determined that this is an instance where the exact conversion should have been used, to avoid making a substantive change in the standard. Thus, in a Federal Register correction notice of September 24, 1998, (63 FR 50995, copy enclosed) NHTSA corrected the measurement in "Glazing surface reference line" to 635 mm (see p. 51000). In changing the measurement from 625 mm to 635 mm, NHTSA stated that: "because the glazing surface reference line centers the windshield wiper path on the windshield, a difference of 10 mm could result in a different wiper path center, substantively changing the Standard." (63 FR 50996). The changes in the correction notice will take effect on May 27, 1999, but immediate optional compliance is permitted as of September 24, 1998.

You also stated that the "inch measurements in tables I through IV appear to be converted at 25.4 mm per 1 inch and then rounded to the nearest full 10 mm." You are correct.

Thank you for bringing this matter to our attention. In the future, it would be helpful if you would provide a mailing address for response. If you have any further questions, please feel free to contact Dorothy Nakama of my staff at this address or at (202) 366-2992.

Sincerely,
Frank Seales, Jr.
Chief Counsel
Enclosure
ref:104
d.3/4/99