Declaration: 
TDataTable.QuartilesOfMarkedCells (LowCol, LowRow, HighCol, HighRow: integer; var Q1, Q2, Q3: double; CellState: byte; var NumData: integer): boolean; 
The function QuartilesOfMarkedCells returns the quartiles in the variable parameters Q1, Q2 and Q3. The calculation of the quartiles is based on the distribution of all numeric cells whose cell state has at least one bit in common with the parameter CellState. Numeric cells are cells which are neither marked as csNAN, nor as csUndefined and which belong to either interval or ratio scaled variables. The cells used for the calculation are limited by the parameters LowCol, LowRow, HighCol, and HighRow. The function returns a FALSE value if any error occurs. The variable parameter NumData returns the number of data points used for the calculation (i.e. the number of numeric data cells within the specified range).

Hint 2: 
Setting both the low and high parameter of a dimension (i.e. LowCol and HighCol) to zero values forces the method to use all elements of that dimension. 
