I have ICL7136 MQFC (the square one) chip driving an LCD display. it's measuring and displaying temperature data from a thermometer probe. I want to grab the analogue readings an log them with an Arduino as well. How what type of setup would yield something usable. Would I just measure from the IN HI or IN LO to the analogue in of the Arduino?
It looks to me like the chip has reference voltage pins and then sensor voltage pins. So it is reading voltage changes from a sensor that reports back in that way, massaging those levels (amplification, scaling, whatever), and then outputting to the display.
Yes, I would think logically reading the same sensor outputs that the chip is reading on IN HI and IN LOW would allow you to access the data. I am assuming the mere act of connecting to those pins and reading them won't change the voltage, but I would defer on that to those more experienced as I could be wrong.
I think your issue, however, is going to be doing the scaling and amplification and conversion of the signals coming in so that the Arduino and the chip both think a given voltage represents the same (in your case) temperature reading. Once they both say that particular voltage level is that many degrees then it becomes a data logging issue.
I wouldn't directly connect to IN LO and IN HI on the ICL7136 unless you haven't got an input filter - as shown in figure 11 the resistor is 1M ohm and an ADC input on an arduino is likely to upset it.
The other issue is the voltages on the two inputs - normally one could be expected to be 0V but this may not be the case so I'd recommend using an instrumentation amplifier to to take the voltage from the thermometer probe directly.
Somethink like an AD8221 but you'll need to generate the appropriate power supply rails for it - you can probably use the power rail for the arduino but you'll likely need a small negative rail unless of course the offset voltage coming from the probe is greater than 2V above 0V.