As we mentioned, chronographs have two different systems for measuring time. And because of this, they also need to show the results of these measurements through indicators. This is not a problem for quartz watches like digital chronographs, but it becomes a problem for analog timepieces, which display this information using hands.
This is why all chronographs have several different sub-dials that help show the results of these measurements - typically two or three in addition to the main dial that shows the time. To indicate the number of subdials, people use the terms BiCompax and TriCompax, depending on whether there are two or three subdials.
On a typical chronograph, there are two second hands. The one on the time side rotates typically in one of the subdials. In contrast, the one on the chronograph side - for the sake of measuring accuracy - is almost always centrally mounted and, when operated, makes one revolution on the dial in 60 seconds. So, you need to have at least one other indicator showing minutes if you want to measure time intervals that fall within this period. And it happens similarly with the number of hours, if you want to go further in measuring longer time intervals.
This means that, usually, a BiCompax chronograph, assuming one of the subdials measures seconds of standard time, allows you to measure a time interval of up to an hour. In contrast, a TriCompax chronograph can go up to a full day of measurement if these subdials are exclusively used for chronograph indications.