This European Standard specifies methods for measuring the level of loss and substantial delay of domestic and cross-border registered letter mail, collected, processed and delivered by postal service providers. The resulting overall figure for loss and substantial delay is expressed as a percentage of the total posted registered mail collected or received by the postal service providers. This European Standard is applicable only to those service providers which have a measurement system in place which - records each item as it is posted, - records each item as it is delivered, - can, by comparing these records, count the number of items which have been posted and not delivered. This European Standard can be used if appropriate to measure the level of loss of other types of postal items for which such a measurement system is in operation. This European Standard specifies requirements for the design and operation of the measurement system and for other procedures to allow the level of loss to be calculated. This European Standard does not specify technical requirements for the design and operation of a registered letter service, except for purposes of measurement. It does not deal with the technical requirements of a track and trace system.