Calculation date and margin of error are displayed when you let the cursor over a watt value.

The last 200m are different since 1993. That's why this common section ends at the crossroads where the 2 routes differ.
For the data before 1990, we use a power 80kg-standard instead of 78kg, because of the equipment & cyclist evolutions.
The 1982 stage is shorter than the others (only 3h30)