Real and planned days in report planning

I define a project with regular planning. Before starting, the initial work plan per month give 16,2 days planned for January (see first copy display). When I keyboard real work allocation on January with 16 days of work for instance, there still are remaining planned days planned 3.8, why ? (see second copy display)
When I keyboard another amount of real work allocation of 16.4 for instance that is greater than the initiate planned day there still are 0.8 remain days? (see third copy display).
Thank by advance for any precisions
Eric

Sorry but I guess I have the response : I have to re compute the planning from February and not January to have consistence data….