One division of the Bhamsha spans 30 degrees divided by twenty seven, which is 1 degree 6 minutes and 40 seconds of arc, 324 divisions in the zodiac. The name carries the reason for the number: bha is the nakshatra, and the twenty seven divisions of a sign answer to the twenty seven nakshatras.
Like the D-7 the division does not come out to a whole number of minutes, so boundaries fall on fractions of a second of arc and two programs can disagree about a planet sitting on a cusp. The ascendant crosses the arc in about four and a half minutes.
The starting sign for the twenty seven-fold count is set by the element of the sign being divided, a rule the classical texts give explicitly. It is not restated here from memory; anyone casting the chart should take it from the text or software in use and confirm the two agree, because the starting rules are not uniform across the sixteen vargas and an error in one produces a chart that looks entirely plausible and is wrong throughout.
The Bhamsha belongs only to the shodashavarga. Its subject is strength and weakness in a general sense, the constitutional resilience of the native, which is why it is sometimes consulted on questions of stamina and vulnerability rather than on any single department of life.