"What are the calculations of a neural network output?"

Hi,

I'm using a neural network to predict a continuous variable. My model is the following:

Node 1 (Sigmoid)
----------------
A -0,311
B -0,183
C -0,391
D -1,448
Bias -2,001

Node 2 (Sigmoid)
----------------
A 0,124
B -0,428
C -0,291
D -3,069
Bias -2,814

Node 3 (Sigmoid)
----------------
A -0,924
B -1,104
C -0,006
D -0,421
Bias -1,557


Output
======

Regression (Linear)
-------------------
Node 1 -0,583
Node 2 -2,161
Node 3 0,88
Threshold 0,533

With this model I want to predict new values, imagine for
A -1,834944684
B -1,754940513
C -0,312412486
D -1,275034298

Rapidminer gives me the result: 15,47%, but I'm not abble to arrive to this solution by the calculations.

My calculations are:

Value of Node 1 = 1/(1+exp(-(bias+sumproduct(coeficients in node 1; new values for A B C D)))
And I proceed similary for the other 2 nodes.

Value of output:
0,533 + (-0,583 )* value of node1 + (-2,161)*value of node2 + 0,88*value of node3
My result is: -88,8%

Can you help me to find my error in calculations?

Thank you very much.

Rufo