In my experiments with Spectrum disk formats I've found myself looking into the ROM code a few times. Several Spectrum emulators have built-in debuggers that let me dissassemble and step through the code, set breakpoints etc.
There are also some fully analysed and commented Spectrum ROM disassemblies available. For the +3 ROM there are fewer though. I've been using this one.
But without the instruction addresses, it's very hard to find the same code in the emulator's debugger that you can see in the commented disassembly.
Having a line number next to every line of disassembly is not the same as having the instruction address. ASM code has comment lines and machine code instructions take variable numbers of bytes of course!
Is there another +3 ROM disassembly available which does include the ROM offsets next to the instructions?