Inventory Management and Control

Introduction

Inventory management is one of the most critical functions of the parts technician trade. It typically represents between 25% and 40% of a dealership's or shop's assets. Poor management leads to hidden costs, stockouts, surpluses, and customer dissatisfaction. For the Red Seal exam, you must master the fundamental principles, calculation formulas, classification methods, and ordering procedures. This chapter covers all evaluated content, including typical traps and calculation tips.

Fundamental Principles of Inventory Management

Objectives of Inventory Management

Inventory management aims to balance two conflicting objectives:

7.Minimize costs: holding costs (warehousing, insurance, interest, obsolescence), ordering costs (labour, paperwork, transportation), and stockout costs (lost sales, work stoppages, emergencies).

8.Maximize service: having the right part, at the right time, in the right quantity, at the right place.

This balance is called the inventory equilibrium point or optimal service level. The service level is expressed as a percentage (e.g., 95% means that 95% of demands are satisfied from stock).

Inventory Turnover Rate

The turnover rate measures how quickly inventory is sold and replaced over a given period (usually one year).

Formula:

Turnover rate = Cost of Parts Sold (CPS) ÷ Average inventory value

Example:

Annual CPS = $480,000

Average inventory value = $120,000

Turnover rate = 480,000 ÷ 120,000 = 4.0

A turnover rate of 4.0 means the inventory is completely renewed 4 times per year. A rate that is too high (e.g., > 8) may indicate frequent stockouts; a rate that is too low (e.g., < 2) indicates overstocking or slow-moving parts.

Days of Supply (or Days of Inventory)

Formula:

Days of supply = (Average inventory value ÷ Annual CPS) × 365

Example:

(120,000 ÷ 480,000) × 365 = 91.25 days

This means the current inventory covers approximately 91 days of sales. The target varies by industry: 30 to 60 days for fast-moving parts, 90 to 180 days for slow-moving parts.

Inventory Classification

Pareto's Law (80/20 Rule)

Pareto's Law states that approximately 80% of the total inventory value comes from 20% of the items. This rule is the basis of ABC classification.

ABC Classification

ABC classification divides inventory into three categories based on annual usage value (quantity sold × unit cost).

Category	% of Items	% of Value	Typical Examples
A	10–20%	70–80%	Engines, transmissions, electronic modules
B	20–30%	15–25%	Alternators, starters, brakes
C	50–70%	5–10%	Bolts, filters, lamps, belts

Calculation method:

33.Calculate the annual usage value for each item: (annual demand) × (unit cost).

34.Sort items by descending value.

35.Accumulate the value and the percentage of the number of items.

36.Assign categories: A (up to 80% of cumulative value), B (up to 95%), C (the remainder).

Practical application:

Category A: strict control, frequent physical inventory (monthly), smaller and more frequent orders, regular parameter reviews.

Category B: moderate control, quarterly inventory.

Category C: simplified control, annual inventory, orders in larger quantities to reduce ordering costs.

XYZ Classification (Demand Variability)

XYZ classification complements ABC based on demand variability:

X: regular, predictable demand (low standard deviation).

Y: seasonal or moderately variable demand.

Z: irregular, unpredictable demand (high standard deviation).

An AZ item (high value, unpredictable demand) requires a larger safety stock than an AX item.

Stock Calculations: Economic Order Quantity (EOQ)

Wilson's Formula (EOQ)

The Economic Order Quantity (EOQ) determines the quantity to order that minimizes total cost (ordering cost + holding cost).

Formula:

EOQ = √(2 × D × S) ÷ H

Where:

D = annual demand (units)

S = cost of placing one order ($)

H = holding cost per unit per year ($)

Example:

D = 1,200 units/year

S = $50 per order

H = $3 per unit/year

EOQ = √(2 × 1,200 × 50) ÷ 3

EOQ = √(120,000) ÷ 3

EOQ = √40,000

EOQ = 200 units

Annual total cost:

Total cost = (D ÷ Q) × S + (Q ÷ 2) × H

= (1,200 ÷ 200) × 50 + (200 ÷ 2) × 3

= 6 × 50 + 100 × 3

= 300 + 300 = $600

Important note: At the EOQ point, the ordering cost is equal to the holding cost. This is an excellent way to verify your calculation.

Reorder Point (or Replenishment Threshold)

The reorder point (ROP) is the inventory level that triggers a replenishment order.

Formula:

ROP = (Average daily demand × Lead time) + Safety stock

Example:

Daily demand = 10 units/day

Lead time = 5 days

Safety stock = 20 units

ROP = (10 × 5) + 20 = 70 units

When inventory reaches 70 units, you place an EOQ order (200 units in the previous example).

Safety Stock

Safety stock protects against demand variations and delivery delays. It is calculated based on the standard deviation of demand and lead time, and the desired service level.

Simplified formula:

Safety stock = Z × σ × √(LT)

Where:

Z = service level coefficient (see table below)

σ = standard deviation of daily demand

LT = average lead time (in days)

Service Level	Z Coefficient
90%	1.28
95%	1.65
97.5%	1.96
99%	2.33

Example:

Z = 1.65 (95%)

σ = 4 units/day

LT = 9 days

Safety stock = 1.65 × 4 × √9 = 1.65 × 4 × 3 = 19.8 ≈ 20 units

Exam trap: Don't forget the square root of the lead time. Many candidates simply use Z × σ, which underestimates the safety stock.

Inventory Valuation Methods

Weighted Average Cost (WAC)

The weighted average cost recalculates the unit cost after each receipt.

Formula:

WAC = (Value of existing stock + Value of receipt) ÷ (Existing quantity + Received quantity)

Example:

Existing stock: 50 units at $10 = $500

Receipt: 100 units at $12 = $1,200

WAC = (500 + 1,200) ÷ (50 + 100) = 1,700 ÷ 150 = $11.33/unit

First In, First Out (FIFO)

FIFO assumes that the oldest parts are sold first. The cost of parts sold is based on the oldest costs, and ending inventory is valued at the most recent costs.

Example:

Purchase 1: 10 units at $10

Purchase 2: 10 units at $12

Sale of 12 units: cost = (10 × $10) + (2 × $12) = 100 + 24 = $124

Remaining stock: 8 units at $12 = $96

Last In, First Out (LIFO)

LIFO assumes that the most recent parts are sold first. This method is prohibited in Canada under Canadian accounting standards (IFRS). It will therefore not be evaluated on the Red Seal exam, but you should know that it exists and why it is prohibited (it distorts the balance sheet during periods of inflation).

Specific Identification

Specific identification is used for unique, identifiable parts (e.g., a complete engine with a serial number). Each part is tracked individually with its actual acquisition cost.

Ordering and Receiving Procedures

Types of Orders

Type	Description	Usage
Direct order	Purchase from the manufacturer or distributor	Fast-moving parts, category A
Emergency order	Expedited purchase, higher shipping cost	Stockout, vehicle waiting
Scheduled order	Planned deliveries at fixed intervals	Parts with regular demand (X)
Automatic replenishment order	Triggered by the system at the reorder point	Computerized management

Receiving Process

119.Verify the purchase order: compare ordered quantity, price, and terms.

120.Physical inspection: verify received quantity, condition of parts, part numbers.

121.Quality control: check for damaged parts, specification errors.

122.System update: enter the receipt into the inventory management system.

123.Labeling and storage: place parts in their designated locations (bin location code).

Exam trap: Receiving must be completed before the inventory update. Many errors come from unrecorded partial receipts.

Returns and Credits

Return procedures include:

Return for credit: unused parts, in good condition, in original packaging, within a specified timeframe (often 90 days).

Warranty return: defective parts, with claim form, original part, and diagnostic report.

Error return: part ordered by mistake, with supplier authorization.

Required documents: Return Merchandise Authorization (RMA), original invoice, proof of delivery.

Physical Inventory and Cycle Counting

Full Physical Inventory

Physical inventory is the counting of all parts in stock, usually once per year. It is mandatory to:

Verify the accuracy of records.

Detect losses, theft, and data entry errors.

Adjust the book value of inventory.

Procedure:

138.Preparation: stop stock movements, print counting lists.

139.Counting in teams of two (one counts, one verifies).

140.Enter actual quantities.

141.Compare with theoretical quantities.

142.Analyze variances and make adjustments.

Cycle Counting

Cycle counting is a continuous inventory method where a portion of the stock is counted at regular intervals. A items are counted more frequently (monthly), B items quarterly, and C items annually.

Advantages:

Less disruptive to operations.

Faster error detection.

Better continuous accuracy.

Variance Tolerance

Variance tolerance is the acceptable percentage of error between theoretical and actual stock. It is generally:

Category	Tolerance
A	± 0.5%
B	± 1%
C	± 2%

Accuracy formula:

Accuracy = (Number of accurate items ÷ Total number of items counted) × 100

An accuracy of 95% or higher is considered acceptable in the industry.

Managing Slow-Moving and Obsolete Parts

Slow-Moving Parts

A part is considered slow-moving if it has not been sold for 12 months or more. These parts tie up capital and increase holding costs.

Strategies:

Reduce safety stock.

Order only on special request.

Negotiate returns with the supplier.

Promote sales (discounts, bundling).

Obsolete Parts

A part is obsolete when it is no longer used by any vehicle in service, or when the manufacturer has ceased production without a replacement part.

Indicators of obsolescence:

No sales for 24 months.

End of vehicle production.

Change in technical specifications.

Treatment:

Write-off from inventory (accounting loss).

Sale at a loss or to a recycler.

Return to supplier if possible.

Computerized Management Systems

Essential Functions

An inventory management system (IMS) must include:

176.Part number management: search by OEM number, internal number, description, vehicle.

177.Stock level tracking: real-time, with replenishment alerts.

178.Purchase order generation: automatic or manual.

179.Traceability: lot number, receipt date, supplier.

180.Reports: turnover rate, inventory accuracy, slow-moving parts, inventory value.

Barcodes and RFID

Barcodes (UPC, Code 128): optical reading, low cost, requires line of sight.

RFID (Radio Frequency Identification): radio frequency reading, no line of sight required, simultaneous multiple reading, higher cost.

Application: Barcodes are the standard in the parts industry. RFID is used for high-value parts or lot tracking.

Canadian Standards and Regulations

Canadian Electrical Code, Part I, Chapter V

The Canadian Electrical Code, Part I, Chapter V (C22.1-21) applies to motor vehicles and off-road vehicles. It governs the installation of electrical systems in vehicles. For the parts technician, this concerns the selection and sale of electrical components (batteries, alternators, starters, wiring).

Rule 8-200: This rule addresses circuit protection requirements. When selling electrical parts, you must ensure that components meet the requirements for current rating and protection.

Practical example: A customer requests a battery for a heavy-duty truck. You must verify the ampere-hour (Ah) capacity and cold cranking amps (CCA) in accordance with manufacturer specifications, which are based on CSA standards.

CSA B149.1 – Natural Gas and Propane Code

CSA B149.1 applies to the installation and maintenance of natural gas and propane appliances. For the parts technician, this concerns parts for alternative fuel systems (tanks, valves, regulators, injectors).

Key requirement: Replacement parts for gas systems must be CSA certified and compatible with the original system. The sale of non-certified parts is prohibited.

Motor Vehicle Safety Regulations (MVSR)

The Motor Vehicle Safety Regulations (SOR/2010-30) from Transport Canada establish the Canada Motor Vehicle Safety Standards (CMVSS). Replacement parts that affect safety (brakes, steering, suspension, lighting) must comply with these standards.

Section 12 of the MVSR: Prohibition on selling parts that render a vehicle non-compliant with the CMVSS.

Traps to Avoid

197.Confusing turnover rate and days of supply: The turnover rate is a unitless number (e.g., 4.0), while days of supply is in days (e.g., 91 days). They are inversely proportional: Days = 365 ÷ Turnover rate.

198.Forgetting the square root in the EOQ formula: The formula is √(2DS ÷ H), not (2DS) ÷ H. Always verify that the ordering cost equals the holding cost at the optimal point.

199.Using selling price instead of cost: The turnover rate uses the cost of parts sold, not the selling price. Using the price artificially inflates the rate.

200.Ignoring lead time in the reorder point: The reorder point always includes lead time. An ROP without lead time causes stockouts.

201.Confusing FIFO and LIFO: FIFO is the accepted method in Canada. LIFO is prohibited under IFRS.

202.Not distinguishing ABC categories: A items require stricter control and more frequent inventories. Applying the same level of control to all items is a management error.

203.Forgetting holding costs in total cost: Total cost = ordering cost + holding cost. Many candidates only calculate the ordering cost.

204.Not checking units: Demand must be annual, ordering cost per order, and holding cost per unit per year. Inconsistent units give absurd results.

205.Confusing safety stock and reorder point: Safety stock is a fixed quantity (e.g., 20 units). The reorder point is an inventory level (e.g., 70 units). The reorder point includes safety stock.

206.Neglecting safety standards: Parts that affect safety (brakes, steering, lighting) must comply with the CMVSS. Selling non-compliant parts is an offense.

Summary

Inventory management balances holding, ordering, and stockout costs to maximize service level.

Turnover rate = CPS ÷ average inventory value. A rate of 4 to 6 is typical for parts.

ABC classification (Pareto) focuses control on high-value (A) items.

EOQ minimizes total cost: EOQ = √(2DS ÷ H). At the optimal point, ordering cost = holding cost.

Reorder point = (daily demand × lead time) + safety stock.

Safety stock = Z × σ × √LT, where Z depends on the service level.

Accepted valuation methods in Canada are WAC and FIFO. LIFO is prohibited.

Physical inventory and cycle counting ensure record accuracy. Target accuracy is ≥ 95%.

Slow-moving and obsolete parts must be identified and dealt with quickly to reduce costs.

Computerized systems (IMS) and barcodes improve accuracy and efficiency.

Canadian standards (Canadian Electrical Code, Part I, Chapter V, CSA B149.1, MVSR) govern the sale of safety parts and specific systems.

Final exam tip: Memorize the formulas by writing them from memory, then redo each example without looking at the solution. On the exam, always write out the units and verify the consistency of your results. An answer with incorrect units is wrong even if the calculation is correct.

Inventory Management and Control