Hi rensdn ,

"AT" represents "Automated Translation", usually by Machine Translation.

I guess you are using both Translation Memory and Machine Translation at the same project.
Trados Studio shows search result by Translation Memory first and they are shown as number of percentage or as "CM".

In case that no search result was found on Translation Memory, result by Machine Translation will be applied. It is shown as "AT".

Hi rensdn 

Unknown said:

How does the location of AT display percentage ？ Or AT and percentage display at the same time?

Most Machine Translation providers display AT only and no percentage.  But it is possible to include a percentage in the result.  For example, this is what we see in an SDLXLIFF using different providers: 

<sdl:seg id="1" conf="Draft" origin="mt" origin-system="SDL ETS translation provider" percent="25">

<sdl:seg id="2" conf="Draft" origin="mt" origin-system="SDL Language Cloud Machine Translation">

<sdl:seg id="3" conf="Draft" origin="mt" origin-system="AmazonTranslate Trados Plugin">

Note that the first one actually includes a percentage and this can be used for filtering results.  The plugin developer did this on purpose to support filtering by fuzzy matches for AT segments.  However, the percentage is not shown in Studio in the column you have highlighted, it's just there in the background and can be used by the display filter.