Figure 7 (page 11) of the USB-6009 manual shows a 127K resistor feeding a 39K voltage centering bias network prior to the Differential PGA. This significantly reduces the input signal voltage (good for 10V into a lower voltage ADC, but poor for low level inputs such as Thermocouple). While planning to reduce this input impedance by a factor of ~10 by paralleling a 14.0K resistor on the 127K (thus upping my input signal significantly), but leaving the 39K, I found another undocumented resistor at the analog input that appears to go to ground. What is the value and purpose of this other resistor?
