Originally Posted by Esteban
Your method will work but - it is better to measure the oil height in the tube rather than the milliliters (CCs) of oil you are putting in. Slight air volume variations have a very noticeable effect of fork function. Measuring the oil height/air volume is a more precise method to achieve desired results.
As Steve indicated, the amount of oil determines the remaining air capacity of the fork. As the air in the remaining "chamber" acts as a spring, the oil level can alter the rate of the air spring... at the very least, getting the oil levels equal is a good thing.
You can also adjust the oil level (within limits) to alter the air spring rate... not the same as changing a coil spring but more of a "fine tune" capability.