What Compare Map is for
Every tuner ends up with a folder of map files: the base map, the first start, the dyno session, the version after the customer's new injectors. Sooner or later you need to know exactly what's different between two of them. Scrolling through every table by eye is slow and easy to get wrong.
Compare Map in NSP loads a second map alongside the one you're working on and marks every setting and table cell that doesn't match. It works on an offline map file and it works while you're connected to a Nexus ECU, so you can check a running car against a saved file without disconnecting.
Two terms matter for everything below:
- Current map: the map already open in NSP, or the one in the ECU you're online with. This is the map you're editing.
- Compare map: the second file you load to check against. It's there for reference.
Starting and stopping a comparison
- Open the map you want to work on, or go online with the ECU. That becomes the Current map.
- Click the Compare Map button on the toolbar, or use File > Compare, then pick Choose Map for Compare.
- Select the second map file and click OK.
- NSP switches into compare mode. The toolbar button now shows which display mode is active, starting with difference values.
- To finish, click the Compare Map button again and choose Exit Compare Mode.
You can change the display mode from the same button with Change Comparison Display Mode, but the quicker way is F9, which steps through the modes.
How differences are shown
Whatever mode you're in, NSP uses purple to flag a mismatch:
- In the navigation tree, any node with a difference is highlighted. Parent nodes light up too when something inside them differs, so you can follow the purple down through the tree to find a change buried several levels deep.
- Inside a settings page, each individual setting that differs is highlighted. Click one and NSP shows both values side by side, with a button that copies the Compare map's value into the Current map.
- In tables, differing cells get a purple border, and axis breakpoints that exist in one map but not the other get a purple label.
That copy button is one of the most useful parts of the feature. If you've got a known-good idle setup in an old map and want just that bit back, you can pull individual settings across without overwriting anything else.
The three display modes
| Mode | Table cells show | Can you edit? | Best for |
|---|---|---|---|
| Difference Values (the starting mode) | Current minus Compare, cell by cell | Yes, edits go into the Current map | Seeing how big each change is, and which direction |
| Current Values | The Current map's real numbers, with changed cells outlined | Yes, edits go into the Current map | Tuning normally while still seeing what's different |
| Compare Values | The Compare map's numbers, with changed cells outlined | No, the table is locked | Reading the other map's values without risk of editing them |
If you're online with an ECU when you start comparing, any edit you make in an editable mode goes to the ECU live, just like normal tuning.
Reading difference values
Difference mode always reads from the Current map's point of view. A positive number means your Current map is higher than the Compare map in that cell. A negative number means it's lower. Zero means they match, and every non-zero cell also gets a purple border so you can spot it quickly.
Say you're comparing today's ignition map (Current) with last week's (Compare), and a cell at high load shows -2. Today's map has 2 degrees less timing there than last week's. If the fuel table shows +5 across a whole band, today's map is carrying more fuel through that area.
In Difference mode, table tools act on the numbers you see, not the real values underneath. Apply a percentage change to a cell showing -10 and the percentage is taken from -10. Linearize a row and NSP spreads the difference across the cells, not the underlying map values. If you want to scale real values, switch to Current Values mode first.
Also note that the 2D and 3D graph views don't draw difference values. They keep showing the Current map's real shape, so don't be surprised when the graph and the grid disagree.
When the axes don't match
Two maps don't always share the same breakpoints. Maybe one has an extra RPM column added during tuning. NSP only does a straight cell-to-cell comparison where the X and Y breakpoints match exactly. Beyond that, what you see depends on which map owns the breakpoint and which mode you're in:
| Breakpoint exists in | Difference mode | Current Values mode | Compare Values mode |
|---|---|---|---|
| Current map only | Label highlighted. NSP interpolates the Compare map's value from neighboring cells to produce a difference | Label highlighted | Row or column hidden |
| Compare map only | Row or column hidden | Row or column hidden | Label highlighted |
The interpolated differences are estimates, so treat them as a guide. If a whole table is shifted onto new breakpoints, the useful comparison is usually the shape of the table in the graph views, not the cell numbers.
Using it to track your own changes
Compare Map also doubles as a simple way to see what you've changed as you go. This is how we use it during a tuning session:
- Save the map you're about to work on.
- Start Compare Map and select the file you just saved as the Compare map.
- Switch to Current Values mode.
- Tune as normal. Every cell and setting you touch now turns purple, because it no longer matches the saved copy.
- When you want a clean slate, save again and repeat the process with the new file.
At the end of a session it's easy to see exactly what you changed, and it's a great way to catch an accidental keystroke in a table you never meant to open.
Where we use it most
- A customer's car came back running differently. Compare the map in the ECU with the file we delivered. If nothing is purple, the problem is mechanical, not the tune.
- Merging work. Pull a proven cold start or idle setup from an older map into a newer one, one setting at a time.
- Firmware and base map changes. See what a new base map actually changed before you trust it.
- Checking a Quick Tune session. Compare before and after to see exactly how far the fuel table moved.
Troubleshooting
| Symptom | Usually |
|---|---|
| Can't type into a table | You're in Compare Values mode, which is read-only. Press F9 |
| Percentage change gave strange results | You applied it in Difference mode, so it acted on the difference |
| The graph doesn't match the numbers | Graphs always show Current map values, not differences |
| A row from the other map is missing | That breakpoint only exists in the map that isn't being displayed in this mode |
| Changes went straight to the car | You were online when you started comparing, so edits write to the ECU live |
Compare Map FAQ
Can I compare while connected to the car?
Yes. The ECU's map becomes the Current map, and any edits you make are sent to the ECU in real time.
Does comparing change either file?
Only if you edit something. Changes always go to the Current map, and the Compare map can't be edited from within compare mode.
How do I switch views quickly?
Press F9 to cycle through Difference, Current and Compare modes. For more NSP diagnostic tools, see the ECU oscilloscope guide, or browse the knowledge base.
