[atlas] Comparison of HW and SW Probes

Hello everybody! Currently, I am investigating the possibilities of measurements using RIPE Atlas. Is there information about differences in the measurement results of HW and SW probes? My advisor said that I should rather not use SW probes, but I am not sure what the actual difference is, especially as SW probes often run on better hardware, compared to the HW probes. Could you point me to some resources on that topic? Best regards, Robert