The distribution chart in TestProject shows a summary the number of tests that have been run on each different agent in your project. This chart is very useful when tests are one multiple agents (for example if multiple team members are running tests on their machines). This chart allows you see if there are difference between pass/fail rates on different agents. This can be really helpful for showing how a particular platform may have issues. For example if you notice that there are significantly more failures on Windows agents as compared to Mac agents, you might want to investigate to see what Windows specific issues there might be.
The distribution chart can be found by clicking on the middle navigation dot under the charts.
These charts are available at the main reports level as a summary view and are also available for each project you have defined