Problem with rectangular grid

Hello, I'm new in the world of Grasshopper and to learn I'm using "Algorithmic modelling with Grasshopper" by Mohamad Khabazi.

My version of Grasshopper is November-08 2013.

In an example, we do a grid with rectangular grid. The result from the tutorial is the following: 

My result is the following:

I don't understand with my grid is not centred at the origin of the plane like in the exemple of the tutoriel. 

I need it to be centred for complete a task.

Thanks for you help.

Louis