I often use this handy tool to debug serial issues: [Device Monitoring Studio: High-Performance Connections Data Logging & Analyzing Software](https://www.hhdsoftware.com/device-monitoring-studio) Despite the fact that it is a paid for product, thier is a "Free" version that has reduced features, but is perfectly usable for basic serial comms spying. If the scale has a sample program with it for example, just run this, attach to the serial port, then run the demo app and see exactly what it's doing, byte for byte. I've used it many times to do exactly that. In one case I figured out that the "visible" commands I could see, where actually all prefixed by a non visible 0x01 byte, and whoever had put the manual together, had not known this byte was in front, and thus just typed the manual up as "ABC..." rather than "0x01ABC" (I was told when I contacted the devices support team to report my findings.) If you elect to go for the paid version, it does all sorts of neat things like Modbus protocol analysis and lot's of other protocol decoders.