differences from first

difference from first calculates the difference between the first and subsequent numerical episodes. For
example, we might define a Calculated Value

DeltaFromFirstHDL = differences from first HDL

This would appear in a case as follows:

               01 Jun 03    20 Jun 03    30 Jun 03    15 Oct 03    02 Nov 03
                 17:29        17:33        20:06        20:06        17:33
HDL               2.0          2.1          2.2          2.5          1.9
DeltaFromFirstHDL   0          0.1          0.2          0.5         -0.1
Trig              3.6                                    3.6
LipidDrug         N                         Y            Y

Note also the following expressions which are true for this case:

max differences from first HDL = 0.5
min differences from first HDL = -0.1

This function can also be used for determining rates of change.