Inventory Accuracy: Building a Stock System You Can Trust

The Inventory Trust Problem

Ask any workshop manager whether their stock numbers are accurate and you will usually get a hesitant answer. Most know their stock records are wrong — they just don't know by how much or in which direction.

This is the inventory trust problem. When nobody believes the stock numbers, the consequences cascade:

• Operators over-request material "just in case"
• Purchasing over-orders to avoid stockouts
• The physical stocktake becomes a painful, reactive event rather than a routine check
• Job costing is unreliable because material usage is estimated

Periodic vs Perpetual Inventory

A periodic inventory system updates stock levels at intervals — weekly, monthly, or during full stocktakes. Between updates, the system's numbers drift further and further from reality. This is the model most workshops operate under, even if they don't call it that.

A perpetual inventory system updates stock levels in real time, every time material moves. When stock is received, it is booked in. When material is issued to a job, it is deducted. When stock is adjusted, there is a reason. The system's numbers are always current because every movement is recorded as it happens.

Perpetual inventory is not a luxury. It is the only model that scales.

Building a Perpetual System

1. Every Movement Is a Transaction

Stock does not just "go down." It goes down because a specific material was issued to a specific job, or because of a documented adjustment, or because of a return. Every movement should be:

• Attributable — who moved it
• Reasoned — why it moved (job issue, receipt, adjustment, scrap, return)
• Timestamped — when it happened
• Referenced — linked to the job, purchase order, or adjustment note

2. Barcode Scanning at the Point of Movement

The single most effective way to maintain perpetual inventory accuracy is to scan material at the point of movement. A barcode scanner at the goods-in area, at the stores counter, and at the shop-floor workstation means material is identified and logged without manual data entry.

Manual entry introduces typos, wrong quantities, and missed transactions. Scanning eliminates those failure modes.

3. Material Issues Against Jobs

When material leaves the stores for a job, it should be issued against that job's works order in the system. This achieves two things simultaneously:

• Stock is deducted — the perpetual record stays accurate
• Job cost is captured — the job's material cost is built up automatically

This replaces the common practice of "bulk issuing" material without recording which job it went to.

4. Cycle Counting Instead of Full Stocktakes

A full annual stocktake is disruptive and, in a perpetual system, largely unnecessary. Instead, implement cycle counting: a rotating schedule where a subset of items is counted each week. High-value or fast-moving items are counted more frequently; slow-moving items less so.

Cycle counting catches discrepancies early, identifies root causes (a scanning error, a mislabelled bin, a training gap), and keeps the perpetual system trustworthy without shutting down the workshop.

5. Reorder Points Based on Real Data

With accurate, perpetual stock levels, reorder points become meaningful. The system can track average usage rates and lead times per item and signal when stock is approaching the reorder threshold — automatically, without anyone having to check.

This transforms purchasing from reactive ("we're out of X, order more") to proactive ("the system flagged that X will hit reorder in three days based on current usage").

Conclusion

Inventory accuracy is not achieved through more frequent stocktakes. It is achieved through a perpetual system where every movement is a recorded transaction, supported by barcode scanning at the point of action. The result is a stock system you can trust, job costs that are real, and purchasing decisions based on data rather than fear of running out.