x# modified: src/docs/part1/simple_detector.md

src/docs/part1/simple_detector.md

@@ -40,6 +40,7 @@ dd_web_display --export gem_tracker.xml
 Copy the generated file `detector_geometry.root` to your local machine.
 Then open the [web viewer](https://eic.phy.anl.gov/geoviewer/), click on the `...` and open the local root file.
 
+Examine the compact description, specifically this part:
 
 ```xml
 <detector id="2" name="GEMTracker" vis="RedVis" type="my_GEMTracker" readout="GEMTrackerHits" > 
@@ -54,12 +55,10 @@ Then open the [web viewer](https://eic.phy.anl.gov/geoviewer/), click on the `..
 </detector>
 ```
 
-
-
 ## Run the geant4 simulation
 
 ```bash
-ddsim  --runType run  --enableG4GPS \
+npsim  --runType run  --enableG4GPS \
    --macroFile gps.mac \
    --compactFile ./gem_tracker.xml \
    --outputFile gem_tracker_sim.root 
@@ -70,20 +69,18 @@ The output will be a root file containing the generated events and GEM tracker h
 
 See the [GPS Documentation](http://www.fe.infn.it/u/paterno/Geant4_tutorial/slides_further/GPS/GPS.pdf) for more information.
 
+## Looking at the data 
 
-## Digitization 
-
-```bash
-root -b -q example_digi.cxx+
-```
-![digi histogram](../example_digi.png)
+First, the data model used by npsim is described here
+https://eic.phy.anl.gov/eicd/
 
-## Channel/Cell Size
+## Hit position
 
 ```bash
-root -b -q example_cell_size.cxx+
-    
+root -b -q scripts/tutorial1_hit_position.cxx
+# note if this fails because of ACLiC, run it again. This is a root bug.
 ```
-![cell size histogram](../example_cell_size.png)
+Look at the generated file in results
+![local hit position](../hit_position.png)