What is the difference between read offset, write offset and the combined read/write offset?

Read offsets occur on reading (extracting). Write offsets happen on writing (burning) a CD-R. Most CD record programs do not support write offsets (as EAC perhaps do not support your writer for burning). So, to create an exact (offset corrected) copy of your CD, you would have to compensate the write offset already on reading. So instead of specifing the read offset as sample offset for extraction, you would rather use the combined read/write offset. This is easily calculated by the formula: Read Offset + Write Offset = Combined Read/Write Offset