Let's say you're tracking your weight. You probably think of your weight as an absolute number that moves around over time. So, you'd send an email to firstname.lastname@example.org with this subject:
Over the next few days, you send in some more stats:
Each time you send a stat you'll get an updated chart back in your inbox. The last chart would look like this:
Relative numbers like +5 and -2 work better when you think of a stat as a series of incremental ups and downs. To reuse the poker example from above, it makes more sense to log how much we won or lost in a session as relative number rather than as an absolute number.
So, you could send several emails with one stat per subject.
Or, you could send several stats in one subject line and separate them with semicolons (;).
poker +167; poker -10; poker -20
poker +15; poker +2
The last chart would look like this: