If you've sat through a planning cycle where someone asks "what's our SOM in the Southeast" and someone else answers with an installed base number, you've watched two different questions get treated like one. They're related. They're not the same, and mixing them up is how a market share slide survives a leadership review and then falls apart in a board meeting.
SOM answers a different question than installed base
Serviceable obtainable market is a forecast. It's the share of a serviceable addressable market a company realistically expects to capture given its channel, pricing, and competitive position, usually expressed as a revenue or unit number over a planning horizon. It's built forward, from assumptions about sales capacity and win rates.
Installed base is a count: how many units of a given machine class are actually running in a region right now, regardless of who sold them or who services them. It's closer to a census than a forecast, a tally of what exists rather than a projection of what might sell.
The confusion happens because both numbers get used to answer "how big is our opportunity," and both show up in the same strategy deck next to each other. But SOM is a share of a forward-looking pie. Installed base is the denominator you'd use to check whether last quarter's unit sales moved your market share at all.
Why OEM strategy teams need both, not one instead of the other
A strategy analyst building a regional plan typically needs SOM to set a sales target and needs installed base to sanity-check the target against reality. If dealer and distributor data suggests 400 active units of a competitor's compact track loader in a three-state territory, and your own SOM model assumes you can convert 150 units next year from that exact pool, the installed base number is what tells you whether 150 is aggressive or has already been exceeded by someone's channel inventory numbers.
Without an installed base figure, SOM floats. It's an assumption stacked on an assumption, usually a top-down percentage of a TAM figure that came from an industry association report nobody can audit. That's fine for a first pass. It's not fine for a board-level market share claim, because the first question back is always "installed base of what, measured how."
This is where most OEM teams get stuck. The honest answer to "how do you know the installed base" is usually a dealer survey, a parts-sales proxy, or a registration-data pull, each with its own gaps. Dealer surveys miss anything that didn't come through your own channel. Parts-sales proxies undercount machines that are serviced independently or not at all. Registration data, where it exists, often lags by a year or trails off entirely outside a few countries that require it.
Getting a defensible denominator without a dealer survey
The analysts who get this right stop trying to make SOM do double duty as an installed base estimate and instead go find the denominator separately, from a source that doesn't depend on who happens to answer a phone survey. High-resolution satellite imagery can give you a site-level count of equipment sitting on quarries, job sites, farms, or yards across a region, then scale that count up with coverage and occlusion correction to a regional figure. That's a different kind of number than SOM. It tells you what's already out there, independent of brand and channel, not what you could win.
Once you have that, SOM stops being a guess layered on a guess. It becomes a forecast tested against a real denominator. "We expect to capture 15% of SOM in this region" means something different when the installed base underneath it is a counted figure instead of an industry-report percentage carried forward from three years ago.
If you're building a regional market share case and the installed base line in your model still traces back to a dealer survey or an association estimate nobody can defend in a review, Installed Fleet Estimation scales site-level machine counts from satellite imagery into that regional figure, with coverage and occlusion correction built in rather than left as a footnote.
Worth a look before your next planning cycle locks the denominator in again.