Many Garmin GPS units have a combination of the letters C, S and X after them. These indicate the following capabilities.

• Colour - that the unit has a colour display
• Sensors - that the unit has sensors such as the bariometric altimeter and electronic compass
• eXtendable - that the unit supports additional memory cards to expand the capacity for maps and other data (note that this only applies to the newer GPSMAP models, and doesn't include some of the older models such as the 12XL)

However, Garmin does not have appear to have used these labels consistently. It is assumed that this is because of marketing and naming reasons.