Decompression plans in DecoPlanner version 4 are sometimes slightly different compared to version 3. What causes this?

Version 3 had a few bugs (i.e., incorrect implementation of the on/off-gassing models) that were fixed in the release of version 4. The majority of these fixes will in some cases result in differences of around 1-1.5% of the dive time. However, one of the corrections can alter the result a bit more. This applies to the rate of helium off-gassing during a surface interval. If you plan repetitive dives with helium, any decompression plan following the surface interval will likely be shorter in version 4 compared to version 3. With this in mind, if you are used to planning repetitive dives in version 3, you would need to increase the conservatism for the repetitive dive in version 4 to achieve the same level of gas loading that you are used to.