While computing approximate natural fundamental time period of the structure using empirical equations provided by IS1893(Part-1)-2016 using clause -7.6.1, effective height of the structure is one of the fundamental parameters to be considered. The code has a clear guideline on this -
This height can be provided by using HT parameter.
It should be noted that there are many situations where HT parameters are to be used along with DX and DZ parameters.