Information/definitions from the Federation of the Swiss Watch Industry FH as found on their official website:

"Chronograph
Watch or other apparatus with two independent time systems: one indicates the time of day, and the other measures brief intervals of time. Counters registering seconds, minutes and even hours can be started and stopped as desired. It is therefor possible to measure the exact duration of a phenomenon. Not to be confused with the timer, the stopwatch and the chronometer."

"Chronometer
Watch which has undergone a series of precision tests in an official institute. The requirements are very severe; a few seconds per day in the most unfavourable temperature conditions (for mechanical watches) and positions that are ordinarily encountered."

"A chronograph is a timepiece equipped with additional time measurement functions independent of normal time-telling."

"A chronometer is a high-precision timepiece which movement, after rigorous testing, has received an official timing certificate from an official timing bureau."

Any seller who is using these terms to describe the watch he/she is offering up for auction should be more than willing to provide proof of these conditions having been met. We say again that a watch with subdials that indicate date, day and month is not a chronograph as some sellers claim and is not a chronometer by Swiss standards. It is just a wristwatch. It may be a very good wristwatch but that's all it is.