When "Blocks" is selected, only blocks with a value in the specified range will be displayed. The upper and lower bounds for this range are determined from the data points.
If "Isosurface" is selected (the default), then an isosurface will be drawn. The value being viewed can be increased or decreased by clicking the Up and Down buttons. This will increase/decrease the current level by a hundredth of the entire range. This can also be accomplished by typing "u" or "d", respectively. To set the isolevel being viewed to a specific value, click on the Set button and enter the desired value when prompted. If there is only one z-level, then the isosurface options will not be available.
Note: the blocks/isosurface option will only display these changes for modeled values not data points .