A shared methodology.
Mastia applies the DECOMP standard. Decomp Finance maintains it and Decomp Academy teaches it. These are the working relationships.
Where the standard lives
Decomp Finance maintains the DECOMP standard and takes modelling and advisory mandates in its own right.
Mastia builds to that standard. Where an engagement calls for modelling capacity beyond one practice, or for a second independent reviewer, they are the first call.
Decomp Academy teaches the standard: modelling fundamentals, advanced project finance modelling, VBA, and in-company programmes for teams that want one shared convention instead of six personal ones.
When a client's own team wants to take a model over properly rather than just receive it, this is where we point them. It is also the honest answer to "could we have built this ourselves?" Usually yes, and here is where to learn how.
These are independent collaborators. Naming them says something about method and nothing about ownership.
A method you can check
Most consultancies describe their approach in terms nobody outside the firm can verify. "Rigorous." "Bespoke." "Best practice." None of those can be tested, which is another way of saying none of them are claims.
Building to a published standard changes that. You can read what it requires, learn it independently, and hold the delivered model against it. If a Mastia model falls short of the standard, that is a finding you can make yourself.