This is correct. The current version only looks at total number of followers. The next version will average the follower count over the age of the account in order to get a (very) rough estimate for the declining influence of inactive followers. (Actually counting the inactive followers would involve too much network activity, so for now an estimate is the best I can do.)

It just occured to me that you weren't talking about network strength in a specififed time. Instead, the rate at which a user gain new followers in different time frames, right?

Yes, I think that's right. Basically, I'll be scoring it based on "new followers per month" on one axis, and "median follower reputation" on the other.

cc: @o1eh, FYI

Here's an example with my account, though the June 30 version will continue to change during the next month:

May 18 version	DRAFT June 30 version (still being revised)