You need a serial to USB converter BUT from the Combro website:


"Why don't you sell the interface cable? When PC's stopped having serial ports our cable worked for a while with a USB to serial adapter. Then the Chinese reinvented RS232 shorting the negative rail to ground. Our cable will work with the more expensive FTDI chip set adapters. There is a theory that the Chinese TTL adapter will work directly with cb-625 if you connect cable SIN to chrono 6V and cable GND to chrono SOUT. I have bought adaptors to test this theory, if I ever get one that is actually recognised by my PC as a USB device, "dee-dum", I will test the theory. "