doc update

docs/manual.md

@@ -831,6 +831,12 @@ So the router will take whatever is not used by the EV box.
 The Zero-Cross Detection (ZCD) module is used to detect the zero-crossing of the grid voltage.
 It is required, whether you use a Robodyn or SSR or any routing algorithm (phase control or burst mode).
 
+When activating `Zero-Cross Detection` in the hardware page, YaSolR will first start a pulse analyzer to grab some statistics about the pulse characteristics: period and length.
+This characteristics are used to fine-tune the TRIAC firing and they can be viewed in the dashboard, in the statistics section:
+
+- `ZCD: Pulse Length` (will depends on your ZCD module)
+- `ZCD: Pulse Period` (should be around 10ms for 50Hz and 8ms for 60Hz)
+
 > ##### TIP
 >
 > The Robodyn includes a ZCD (its ZC pin).