01 · Log it
Capture a clean factory pull on the road you will use again. Idle first, then the pull. Put the job on the desk before you touch the file.
Method
Same vehicle, same stretch, factory log then modified log. The overlay is how the shop shows the owner what changed.
A job
Capture a clean factory pull on the road you will use again. Idle first, then the pull. Put the job on the desk before you touch the file.
Calibration, DPF / EGR / AdBlue work, or both. Intended use is the customer’s. We do not write a sheet that hides the work.
Modified log on the same stretch. Overlay factory against modified.
Print the customer sheet. Save the job pack with the logs and the work you did.
What Desk computes
Attach the factory and modified pulls to the job. Desk reads the traces and produces the overlay — estimated wheel power in kW and torque in Nm, on the same rpm axis as boost, injection, rail and EGT.
Mass on the job card is required. Both logs run through the same calculation so the overlay is a comparison, not two different methods. Nothing is typed in after the files are on the job.
The printed sheet labels those figures as a road-load estimate — the honest name for a number taken from a road pull.
Road-load calculation
Road-load power is calculated from the forces the vehicle must overcome while accelerating. Desk does this from the log. The shop does not type the number in.
Basic relationship
v is vehicle speed. Ftotal is the sum of the resistive forces.
The forces
Mass times measured acceleration from the speed log. This is the useful part for a power measurement.
Air density, frontal area, drag coefficient and speed squared.
Mass, gravity and a tyre rolling-resistance coefficient.
Mass, gravity and the sine of the road angle. Zero when the grade is not known.
What Desk does
Desk takes the logged vehicle speed, differentiates it to get acceleration, applies the fixed vehicle mass and the stored CdA / rolling model, then multiplies the resulting force by speed to get power.
Torque is derived from that power and engine speed, with gear ratio and tyre size. Results are normalised to a reference day — temperature and atmospheric pressure — so different pulls can be compared.
The model is fixed. The only inputs that change between pulls are the measured acceleration and speed. That is why small differences in grade, wind or driving style still appear in the numbers, even on the same road.
Coverage
Desk is in active workshop use. A new vehicle or a new log format gets proved on that job, then it stays in the book.