Temperature offset on HP laptop

I am trying to log temperature data with a Pico TC-08 data logger. I am using the RS232 port to connect the logger to the laptop. When conducting zero tests I get an offset of 12 degrees C with the one logger and 2 degrees C with the second logger. These offsets are not a problem when I use a different laptop. I have read that earthing problems might be causing this offset. It is suggested that the port is manually earthed. How does one go about doing this?

Do you have any other suggestions why the loggers work on one computer but not the other?

I have read that is it possible to connect more than one logger to a single computer. Is it as simple as getting an RS232 splitter, connecting the loggers, setting them up and logging?

Thanks,
Tim

That looks like an earthing issue.

Connecting multiple TC-08's is possible but each one will need it's own serial port, a splitter will not work.