Type in your desired series of increments, then press "Run". Remember that your series should always end in 1.
You will then see the cost for Shellsort on your set of increments, and also the cost for a regular Insertion Sort and the cost for the "divide by 2" increments.
You can set the input size. Run this on some bigger inputs to get a more realistic idea of the costs.
Your goal is to come up with an increment series that needs fewer comparisons and swaps than the "divide by 2" series.