39 CFR § 3055.20 - First-Class Mail.
(a) For each of the Single-Piece Letters/Postcards, Presorted Letters/Postcards, and Flats products within the First-Class Mail class, report the on-time service performance (as a percentage rounded to one decimal place), disaggregated by mail subject to the overnight, 2-day, 3-day, 4-day, and 5-day service standards, as well as in the aggregate for the 3-to-5-day service standards.
(b) For each of the Outbound Single-Piece First-Class Mail International and Inbound Letter Post products within the First-Class Mail class, report the on-time service performance (as a percentage rounded to one decimal place), disaggregated by mail subject to the 2-day, 3-day, 4-day, and 5-day service standards, as well as in the aggregate for the 3-to-5-day service standards and in the aggregate for all service standards combined.
(c) For each product that does not meet its service goal during the reporting period, report the point impact data for the top ten root causes of on-time service performance failures, at the Postal Administrative Area and National levels, during the previous fiscal year. “Point impact data” means the number of percentage points by which on-time performance decreased due to a specific root cause of failure. Identification and a description of all potential root causes of failure assigned during the previous fiscal year and any changes to the Postal Service's methodology for calculating point impact data shall be included.