# Tags

## What are tags?

Tags are simply reference numbers that indicate that a certain event occured.

## Why would I use tags?

Tags are useful to record when something happened in your QCM200 experiment. For example, if you zero the relative resistance to the current value, you may wish to know when this occured when analyzing your data. The QCM200 software takes care of this by automaticaly assigning a tag value of 2 to the log file. Even if you aren't logging the data, the display will show you when this event occured with a marker on the chart.

## What are the tag values?

### Tag Level 1

Tag Level 1 corresponds to the Zero Rel F button being clicked. It means that the relative frequency measurement has a new reference value. The new reference will be used for new data only; the old data is not recalculated to this new reference.

### Tag Level 2

Tag Level 2 corresponds to the Zero Rel R button being clicked. It means that the relative resistance measurement has a new reference value. The new reference will be used for new data only; the old data is not recalculated to this new reference.

### Tag Level 3

Tag Level 3 corresponds to both the relative frequency and relative resistance measurements getting a new reference value. (See above).

### Tag Level 4

Tag Level 4 corresponds to a User Tag. User Tags are required to record when events outside the QCM200 software occur (injection of new fluid into the flow cell, stirring begins or ends, heating begins or ends, and so on).

### Tag Level 5

The highest level of tag, value 5 is only recorded in the log file. When a log file begins, some reference values are required for the relative frequency and relative resistance modes. The values used are the ones measured when logging begins.
This can sometimes confuse users when they start logging after running for an extended period of time. All of a sudden, their relative frequency (or resistance) goes to zero! This is because the log file re-zeroes the relative F and R when it begins.