And some toggle views over it...
Firstly, showing lap deltas from one lap to the next (that is, the time difference between each lap and the previous lap in the stint), except for the first full lap of the stint, for which the laptime is displayed:
On the lap delta view, a stint with a constant run of red 0.1 values shows that a driver's time is getting worse (increasing by +0.1s) per lap. A run of blue -0.1 values would show he has getting 0.1 seconds faster on each lap.
Secondly, using stint gap, taken as the time difference between a lap and the first complete laptime from that stint. If you look carefully, the stint gap times are displayed using italics as a point of difference from the lap-delta view. If a driver was getting 0.1s worse per lap in a stint, the numbers would increase 0.1, 0.2, 0.3,... lap on lap. As with the lap-delta view, the actual laptime for the first complete lap in the stint is displayed in full. The stint gap times show the difference between this first stint lap reference time and the laptime for a lap later in the stint.
[On my to do list are some annotations to the chart, to include things like the total number of laps run in the session by any given driver, and perhaps the gap to the session best overall laptime as well as the gap to the car classified one position ahead. And I still need to sort out the ordering!]