AD698 output minimum voltage problem

I choose AD698 sealed with 28 pin patch, which needs 0~10V output for single power supply(24V). The circuit is built according to the data schematic diagram, and R6 and R5, the resistor connected to OFFS1 OFFS2 pin, cannot make the output voltage drop to 0V at least, but only reach 4V at least. What is the reason for this?