Step 5: C3 = 1KV 5.6pF Capacitor
This capacitor has a lot to do with the output range of the ArduiNIX Shield. If you want approximately 100V-200V output, use the 5.6pf capacitor. If you want a greater range, try a 47pF capacitor (not provided for C3) for approx. 200V-300V.
This capacitor can be placed in either direction, it is not polarized.