The function cumulative doesn't have a correct behavior.
As definition the cumulative function sums the Series values starting from the first point. Example: Given these values: 1 2 3 The TCumulative function returns: 1 3 6 ( 1=1, 1 2=3 and 1 2 3=6 )"
In this case, I understand if I am working with a range the function should sum the values of range, should accumulate only these and should reset to zero when you start a new range values. For example, if you have 7 5 6 8 2 and range is 2, the result are expect is that  7+ 5=12  and 6 +8=14. Currently but, the result isn't it, so, the function when range is 2, sum every 2 values, obviate the intermediate values and don't reset the acumulate values to 0. The results is 7 6=13 and 7 +6 +2=15.  Therefore, I consider the funcionality of current function cumulative is incorrect. 
To check exactly the problem, you can reproduce it in a easy way using demo project and following next steps:
1.- Open Demo All features\Functions\Extended\Cumulative
2.- Open Editor and change NumofPoints to Range=2
3.- See the result as you get. 
This problem occurs in Net  with number [TF02016384] and in Java with number[TJ71016386].  [created:2012-10-10T13:58:14.000+01:00 reported by:sandra@steema.com reported in version:]