It seems to just be a calculator, not a split calculator. In other words, when I asked for 100m splits for a 56sec 400m, it simply divided by four and gave all four splits as 14secs. This is not a good race model. Do races longer than 400m, such as the 800m, 1600m etc. utilize evenly paced splits for all segments of the race? Even so, if you want, for example, 100m splits for the 1600m just divide your target time by 16 and there ya go.
A more useful calculator would be one that calculated splits based on best race models. For the 400m in 56secs, are the best 200m splits 26.5/29.5secs or 27/29? What are the target 100m splits?
Different calculators and tables give quite different results.