Interpretation of stock control diagrams
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A stock control diagram illustrates the flow of stock (inventory) into and out of a business over time
Example stock control diagram

Diagram analysis
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The maximum stock level is the maximum amount of stock a business is able to hold in normal circumstances (1,600)
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The reorder level is the level at which a business places a new order with its supplier (800)
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The minimum stock level is also known as the buffer stock level and is the lowest level to which a business is willing to allow stock levels to fall (400)
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The lead time is the length of time from the point of stock being ordered from the supplier to it being delivered (one week)
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The stock level line shows how stock levels change over the given time period
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As stock is used up, a downward slope is plotted
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When an order is delivered by a supplier, the stock level line shoots upwards
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Worked Example
The diagram below shows stock movements of kitchen shelving units sold by TamFix Ltd.

Identify the following points:
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The minimum stock level
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The reorder level
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The reorder quantity
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The lead time for kitchen shelving units (4)
Step 1: Identify the minimum stock level
The minimum stock level is identified by the bottom-most dotted line. In this case, it shows that the minimum stock level is 200 units. [1]
Step 2: Identify the reorder level
The reorder level is clearly identified on the diagram. In this case, it shows that the reorder level is 500 units. [1]
Step 3: Identify the reorder quantity
The reorder quantity is the difference between the maximum stock level (shown by the topmost dotted line) and the minimum stock level.
1,000 units (maximum stock) − 200 units (minimum stock) = 800 units
The reorder quantity is therefore 800 units. [1]
Step 4: Identify the lead time for kitchen shelving units
The lead time is the difference in time between an order for stock being placed and its delivery. In this case, assuming a five-day working week, the lead time for shelving units is two days. [1]
Buffer stock
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Buffer stock is a quantity of goods/raw materials kept in case of stock shortages
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This can provide a competitive edge over rivals unable to meet demand
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This approach is commonly called “just in case” stock control
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The decision to keep buffer stocks is one that businesses have to weigh up very carefully
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The decision will be influenced by the nature of the business and the product/service it provides
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Advantages and disadvantages of holding buffer stock
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Implications of poor stock control
Too much or too little stock: implications

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Problems may arise from holding too much stock
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Storage costs (e.g. warehouse rental, security costs) will be higher than necessary
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The risk of spoilage and stock shrinkage will be increased, leading to increased costs
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Similarly, holding too little stock is risky
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A business may run out of stock, resulting in production stoppages and higher unit costs related to underused capacity
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A sudden increase in demand may not be capable of being met, which leads to a loss of potential sales revenue
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Just-in-time stock management
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Just-in-time stock management is a process in which raw materials are not stored on-site
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Stock is ordered as required and delivered by suppliers “just in time” for production
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Careful coordination is needed to ensure that raw materials and components are delivered by suppliers at the moment that they are to be used
Advantages and disadvantages of just-in-time stock management
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Waste minimisation
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Waste in a business can occur for a number of reasons
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Stock becomes obsolete unless used by a particular date
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Perishable stock (food and medicines) that is not used before it deteriorates will need to be thrown away
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Stock may be damaged as a result of poor storage conditions and may not be suitable for use in the production process
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Allowing waste to go unchecked will increase the unit costs of production and reduce both efficiency and productivity
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Businesses may take a range of steps to minimise waste
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