how fast they are typing overall. Most people have specific letters that take longer to find or get to than their average seek-time for all letters. Which letters vary dramatically and consistently for different people. Right-handed people may be statistically faster in getting to keys they hit with their right-hand fingers than with their left-hand fingers. Index fingers may be characteristically faster than other fingers, consistent for a person regardless of their overall speed that day. In addition, sequences of letters may have characteristic properties for a person. In English, the word "the" is very common, and those three letters may be known as a rapid-fire sequence and not as just three meaningless letters hit in that order. Common endings, such as "ing", may be entered far faster than, say, the same letters in reverse order ("gni") to the degree that varies consistently by a person. This consistency may hold and reveal the person's native language's common sequences even when they are writing entirely in a different language, just as revealing as an accent might in spoken English. Common "errors" may also be quite characteristic of a person. There is an entire taxonomy of errors, such as this person's most common "substitutions", "reversals", "drop-outs", "double-strikes", "adjacent letter hits", "homonyms", hold-length-errors (for a shift key held down too short or too long a time). Even without knowing what language a person is working in, these errors might be detected by looking at the rest of the text and what letters the person goes back and replaces. Again, the patterns of errors might be sufficiently different to distinguish two people. Authentication versus identification Keystroke dynamics is part of a larger class of biometrics known as behavioural biometrics, a field in which observed patterns are statistical in nature. Because of this inherent uncertainty, a commonly held belief is that behavioural biometrics are not as reliable as biometrics used for authentication based on physically observable characteristics such as fingerprints or retinal scans or DNA. Behavioral biometrics use a confidence measurement instead of the traditional pass/fail measurements. As such, the traditional benchmarks of False Acceptance Rate (FAR) and False Rejection Rates (FRR) no longer have linear relationships. The benefit to keystroke dynamics (as well as other behavioural biometrics) is that FRR/FAR can be adjusted by changing the acceptance threshold at the individual level. This allows for explicitly defined individual risk mitigation–something physical biometric technologies could