The three inputs
Billboard converts everything into equivalent units. Roughly: 1 album sale = 10 song streams = 3,750 audio streams of a full album. The Hot 100 weighs sales, on-demand streams, and radio airplay — each measured by different data partners.
Why the cutoff matters
The tracking week is a fixed Friday-to-Thursday window. A purchase logged one minute after Thursday's cutoff counts for the following week. That's why fan orgs coordinate exact purchase timing to concentrate units into one week and maximize peak position.
In-store vs online
Different retail feeds report on different schedules. The tweet's warning — buy in store for the first tracking week — reflects that some online orders don't clear reporting until the item ships, pushing the sale into a later week.
Streams have a ceiling
Billboard caps how many streams from a single account count, to stop bots and looping from distorting the chart. Genuine reach beats raw repetition — one song across many listeners outscores one listener replaying it endlessly.