# Author Archive | Don Johnston

## Open Source Service Level Measurement Software

Open source service level measurement software is now available. For details, click on the “SIMS” tab. For information about the technique which the software uses to measure overall service level, see my article on that subject.

## Service Level Measurement

I will consider two definitions of service level. One is the probability that the next customer demand will be supplied immediately off the shelf. This definition is often used in theoretical work. It is applicable to both individual items (products) and the entire inventory. It can be considered to be the instantaneous service level because […]

## Open Source ABC Analysis Software

Open source ABC analysis software is now available. For details, click on the “SIMS” tab. For information about ABC analysis, see my article on that subject.

## Exponential Smoothing and Inventory Management

The technique described here is called “exponential smoothing”. It is a simple method of updating an average as new data becomes available. It is the basis of most techniques used for forecasting customer demands. It was discussed briefly in the article entitled “Demand Rate Estimation”. In this article, it will be illustrated in relation to […]

## Bugs Fixed in Simulation Spreadsheet

Some incorrect formulae were found in the simulation spreadsheet described in the article entitled “An Educational Inventory Management Simulator“. They have been fixed.

## Lead Time Analysis – Part 2

This article contains information concerning the mathematics involved in the spreadsheets which are described in Part 1. That article was revised on 5 March 2017 and the spreadsheets were revised on 19 February 2017. It is assumed that the readers of this article have some knowledge of statistical mathematics. Any row which is concerned with […]

## Lead Time Analysis – Part 1

Replenishment decisions rely on forecasts of lead times amongst other things. If the mean lead time for an item is not expected to change much then the average of recent lead times for the item can be used. Unless that item is purchased frequently, there won’t be many lead times to use for averaging purposes. […]

## Principles of Good Inventory Management

It is easy to reduce investment in inventory if you don’t mind a deterioration in customer service. Likewise, it is easy to provide good customer service if you don’t mind having a large investment in inventory. Good inventory management is concerned with having a low investment in inventory in relation to the customer service provided […]

## An Educational Inventory Management Simulator

I have developed an inventory simulation spreadsheet for educational purposes. It provides two facilities which are not provided by the online simulator which is accessed by means of the “Simulator” tab. The additional facilities are graphs and use of your own demand history. The online facility is more versatile than the spreadsheet. Also, it carries […]

## Monte Carlo Simulator – Part 2

This article contains detailed information concerning the online Monte Carlo inventory management simulator which can be accessed by clicking on the “Simulator” tab in the menu at the top of the page. In parts of this article, it will be assumed that the reader has some knowledge of statistics. If you don’t have a statistical […]