Is that after Rosie had been working for 4 weeks or after 3 years?
Peacetime employees often had to "master" a number of different jobs as few aircraft factories actually had "assembly lines". Planes were built in batches, some of them rather small with little in the way of the production tooling and jigs that would be used later. Wartime large production runs often saw the same worker doing the same job (riveting a certain section of aircraft?) for months on end. With accurate jigs to hold parts in place and accurate templates to go by.