I hopefully make it clear that No Game System has a copyright in using Economics used as a World building tool. That said, you can use GDP and GDP/C to mark Technological Advance since this represents Productivity. Its easy to make your guideliness and work the numbers back and forward.
This leads me to another Technological Indicator: the Cost of Energy and the Future.
Currently in this Technological Era the cost of 1MW is $2M. In Traveller's TL10 1MW is $200k. In my calculations to make space shipping more cost efficient, in my previous posts, the cost should be 1MW is $40k.
TL is used here to mark a level of GDP/C level of productivity.
TL or Era and the Cost of Power for 1MW
6 $50M (renewable); $1,250,000 (non-renewable)
7 $10M (renewable); $250,000 (non-renewable)
8 $2M (renewable); $50,000 (non-renewable);
9 $400k (renewable); $10,000 (non-renewable)
10 $80,000* (renewable); $2,000 (non-renewable)
You will notice that TL 6, 7, and 8 occur about the course of 100 years and all tech advances are much slower. It is not a fair assumption to think that the rate of growth in the 20C and the start of the 21C will be the same. These are rates of growth and they can be malleable depending on the setting and situation; what is the "Snapshot" GDP/C in a given timeline. Imagine GDP/C as a diagonal line, instead of a curve and that is what measures technology. The rates can change in various setting; Vilani Imperium had extraordinary GDP/C growth in their earlier eras and slowed down in 2170CE, while we are experiencing a slow down right now in our own TL regarding renewable energy.
You can have setting stretch out their TL5, or TL6, or TL7 because of the many hindrances that are affecting their science (like what is happening now with the many science hindrances; the anti-science possibility we have today thanks to politics and those who muddy the water).