Added some comment on the data to the data README.

data/README.md

@@ -15,6 +15,17 @@ Two new data structs then appear in the workspace
 - `simulated_pos_ol_response`
 - `measured_acc_ol_response`
 
+The first two data structures contain (vertical) positions of the three levels/stages: 
+
+- `zr` for the road level,
+- `zus` for the suspension level, 
+- `zs` for the car level.
+
+Strictly speaking, just `zr` and `zs` are measured by their dedicated sensors. The absolute position `zus` 
+is inferred as a difference between `zs` and yet another encoder measurement `zs-zus`.
+
+The third data structs contain just the acceleration of the car level, that is, `d2/dt2 zs`. 
+
 Plot these using
 
 ```matlab
@@ -46,4 +57,4 @@ You will get something like the figures below
 ![figures/simulated_pos_ol_response.png](figures/simulated_pos_ol_response.png)
 ![figures/measured_acc_ol_response.png](figures/measured_acc_ol_response.png)
 
-See the corresponding Simulink file for the meaning of the stored variables.
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+Apparently, the simulation responses do not quite fit the experimental ones. Some optimization-based fitting might be needed here.
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