Abstract
Ringing operations hold opportunities for introducing error into biometric recording. This situation needs to be addressed by field workers, data processors and archivists. Avoidable error may be systematic and/or random, and adds "noise" to random error from natural variation. Handling techniques and measuring equipment are responsible for introducing systematic errors in fieldwork. This aspect requires an increased level of professionalism among ringers to correct it. Analysis of data can induce further random error, e.g. when generating indices from measurements. Analysts also need to be aware of pitfalls inherent in field data, especially that collected historically.