Before reading this article, be sure you understand the differences between listens and subscribers.
You may notice that your subscriber counts vary day-to-day. This is normal, and is a result of how subscribers are counted.
Pinecast does a direct measurement of the number of unique subscribers accessing your feed. There's no way to actually measure the number of people that press a "subscribe" button somewhere (there's no "ping" that gets sent out from podcast apps). Instead, Pinecast measures the number of times each feed gets downloaded with a unique device fingerprint each day, which closely corresponds to the number of subscribers that each feed has. If we see ten unique devices hit a feed, we report ten subscribers for that podcast.
This number varies because it's an actual discrete measurement, not a continuous count. That is, the number resets to zero and counts up each day, rather than starting from the previous day's value and increases or decreases. If one of your subscribers, say, has their phone turned off for a full day, they won't be counted as a subscriber for that day because their device did not download your feed.
You will likely notice a weekly pattern. Depending on your audience, you may see a bump in subscribers during the week as they check your feed on their commutes, or on the weekend when they use their home desktop computers.