Do you want it to only rotate exactly 2.5 deg in either direction or by any increment up to 2.5 degrees in either direction.
The reason I ask is because there is 3 settings which you can have on the dynamic block.
1) None - you set the minimum and maximum amount of rotation
2) Increment - you set the increment you want the thing to be rotated i.e. 1 deg, 5 deg etc. , can be up to 359.99~ deg.
3) List - you specify a list of angles that it can be rotated i.e. -2.5, 0, 2.5
To set the rotation style and/or increments, using bedit, highlight "Angle", this is your "rotation parameter". Right click and select properties. In the properties window, under "Value Set", select Ang type and set the type of angle you want. Depending upon the type of angle, you will need to enter the values below accordingly.