## BCal help system: The Tutorial |

A group is an archaeologically coherent collection of related determinations. In most cases a group will represent an archaeological phase or sequence. In our example, we have 3 phases, but only two of them contain determinations. This means that we are unable to express Layer I as a group. Layer I does not give rise to any radiocarbon information or any absolute chronological information on the calendar scale and so we can leave it out of the BCal definition altogether. Thus we have two groups that we wish to investigate within BCal and should enter this into the "Number of groups" field.

Floating parameters is a BCal concept that may, at first, be a little
tricky to understand. Such parameters are used to represent an event
within the chronology about which we have absolute *a priori* chronological
information but no radiocarbon information. In our example, the arrival
of the Polynesians may be represented by a floating parameter. We
know how this event fits into the chronology, i.e. the event is earlier
than the start of Layer II. We also have absolute *a priori*
chronological information about the event, i.e. the date of the event is
normally distributed with a mean of 600 AD and a standard deviation of
100 calendar years. However, we do not have an organic sample that
dates precisely to this event. Thus we have one floating parameter and
should enter this number into the "Number of floating parameters" field.