Tooltips
Hovering the mouse cursor over a calendar square will show the details (tooltip) for that day’s workload for a given issue (IMPORTANT: in order to show the tooltip, the “Show labels” option must be checked in the “options” button).
So, for May 8 and for issue WP-6, user “Xavi Alonso” has 8 hours available and the workload for that issue on that day is 2.3 hours, in other words, 2.3/8=0.29 → 29% Idle
The row for the user reflects each day’s total workload as the sum of partial workloads for all the issues assigned on that day.