Updated description of the way Segment calculates timestamps

Author: markzegarelli

src/connections/spec/common.md

@@ -395,6 +395,8 @@ The `receivedAt` timestamp is most important as the sort key in Segment's Wareho
 
 ### timestamp
 
-The `timestamp` timestamp specifies when the datapoint occurred, corrected for client-device clock skew. This is the timestamp that is passed to downstream destinations and used for historical replays. It is important to use this timestamp for importing historical data to the API.
+The `timestamp` timestamp specifies when the data point occurred, corrected for client-device clock skew. This is the timestamp that is passed to downstream destinations and used for historical replays. It is important to use this timestamp for importing historical data to the API.
 
-If you are using the Segment server Source libraries, or passing calls directly to the HTTP API endpoint, you can manually set the `timestamp` field.  If you are using a Segment Source in device mode, the library generates `timestamp` and you cannot manually set one directly in the call payload.  
+If you are using the Segment server Source libraries, or passing calls directly to the HTTP API endpoint, you can manually set the `timestamp` field. This change updates the `originalTimestamp` field of the Segment event. If you use a Segment Source in device mode, the library generates `timestamp` and you cannot manually set one directly in the call payload.  
+
+Segment calculates `timestamp` as `timestamp = receivedAt - (sentAt - originalTimeStamp)`.