Production & costing
Sales, purchasing, production, stock, and cost in one ledger — replacing a rigid legacy ERP without giving up the accounting discipline that made it trustworthy.
The situation
A manufacturer running a legacy ERP that was, to be fair to it, accurate. It was also immovable: changing anything meant working against the system rather than with it.
So people worked around it instead. Spreadsheets appeared beside the ledger, and a gap opened between what the software said and what the shop floor knew — and on the details that mattered, the shop floor was usually right.
The quiet failure
An ERP nobody can change stops being the system of record. It becomes one more opinion about what happened.
Cost is the hard part. Stock on hand, unit cost, receivable balance, and gross margin cannot be stored as columns — columns drift, and once they drift nobody trusts the report again. The correct model is the one the legacy system got right: a document never stores its effects, it posts immutable movements, and every balance is an aggregate over those movements.
Sales, purchasing, production, stock, costing, and reporting rebuilt around a posting engine, with the cost calculation implemented as pure, unit-tested functions rather than logic buried in screens. Period-close snapshots keep it fast without reintroducing values that can drift. The rigidity went away; the discipline did not.
Scope
Working principle
A document never stores its effects. It posts movements.
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