The only other point is... If you are actually taking about Speed through the Water, you should calibrate the unit, if it is new or never calibrated. Preferably on a measured mile to be most accurate (Normally measured miles are around commercial
You basically make 3-4 passes up and down a measured mautical mile telling the unit each time when you start and stop. It averages out the distances and calibrates to your actual speed through the water in knots. There are also other ways of calibrating speed with the ST-60, but this is the most accurate. For detailed instructions refer to your Raymarine Owners Manual.
The Speed over Ground does not need to be calibrated since it is calculated by using your relative position via GPS.