What if I want to learn more about a specific Twitter account's reach?

There are three ways to learn more about the reach of a particular Twitter account, depending on the type of information you're looking for. 

1. Run a report for a username. Do not include the @symbol. See this report for unionmetrics. 
   This report will return all mentions of that Twitter account (including all types of retweets and mentions), as well as all tweets from that Twitter account. This is the most comprehensive set of reach stats for a Twitter account. We call this the From and About report, because it returns data both from a Twitter account, as well as about a Twitter account. 
2. Run a report for a username and include the @symbol. See this report for @unionmetrics. 
   This report will return all mentions of an account, but not any tweets from that account. This report will let you know how many people are talking about a certain Twitter account, and the ways they're talking about it (manual retweets, replies, mentions). We call this the About report, since it only returns tweets about an account from other Twitter users.  
3. Run a report using the from: operator and a username. Do not use the @ symbol. See this report for from:unionmetrics. 
   This report will return only tweets from that account. This reports is useful for measuring the reach of an individual Twitter account, and for learning more about the kinds of tweets that account is posting. We call this the From report, since it only includes tweets from that Twitter account. 
4. Run a report using the from: operator and the phrase "RT @username". Separate the terms with the OR operator. See this report for from:unionmetricsOR "RT @unionmetrics".
   This report will return tweets from that account, as well as any retweets of that account. This is useful for measuring the impact of an account's tweets and its retweets, without including other mentions or replies. We call this the Retweet report, since it include original tweets and retweets.  

Note: Usernames with underscores in them need a special query. Instead of searching for the bare word username, you'll need to search for @username OR from:username (a combination or 2 and 3 above).