Your MES knows what happened at 2 a.m. ERP does not. That is the short answer on MES vs ERP: ERP records the plan and the money, the order, the cost, the promise date, while the MES records the events on the floor, the run, the stop, the count, the timestamp. Neither one records why it happened, and why is the part you actually needed. Here is a conversation I have had, in some form, more than once. A quality manager has two windows open to answer one customer question. Why did lot 4471 ship two days late. ERP told her the order was released on the 6th and shipped on the 12th. The MES told her the line stopped for 41 minutes on the night of the 9th, reason code Other. To get the rest she phoned a supervisor at home on a Saturday. He remembered. The seal bar had been drifting all week and the night crew had a workaround nobody had written down. What ERP actually records ERP, the enterprise resource planning system, is the record of what you meant to do and what it cost you. It tracks the order, the part number, the bill of materials, the vendor, the lot, the invoice, the promise date. It handles planning, purchasing, releasing, receiving, costing, shipping and invoicing. It is very good at those. Ask ERP what a lot cost, who it went to, and what it consumed, and you get a clean answer with a number on it. Ask ERP what the line was doing between 02:00 and 03:00 and it has nothing to say, because it never recorded anything at that level of detail. In ERP, the order was open, then it was closed. What your MES actually records The MES, the manufacturing execution system, is the record of events on the floor. It tracks the machine, the work centre, the operator, the batch in progress, the count, the stop. It records starts, runs, stops, scrap, holds, releases and changeovers. It knows the line stopped at 02:14 and restarted at 02:55. That part is machine-generated and it is usually right. Whether it knows why is a different question, because the reason is a dropdown somebody picked at three in the morning with a line to restart. In most plants I hear about, the stop reasons pile up in the same three codes, and one of them is Other. So both systems fall short, in different ways. ERP does not record at the level of a single hour. The MES does, but it records the reason using a list of codes somebody chose when the software was installed, years before anyone knew what would actually break. What the MES vs ERP comparison leaves out MES vs ERP is usually argued as a buying question, which system to put in and what it costs. The more useful question is which record is missing from both. You have a record of what you planned and a record of what happened. What you do not have is a record of why it happened. Neither system records what people worked out. Neither one records that the seal bar had been drifting all week, that the night crew had a workaround, that the same thing happened in March and someone solved it then too. That record does exist. It is in the heads of three or four people, unevenly, and it is not written down anywhere. The reason it stays there is organisational, not technical. ERP reports to finance or IT. The MES reports to operations or engineering. The ERP and MES integration was scoped, correctly, to move quantities and order status. Nobody wrote a requirement for recording why, because recording why was never anyone’s job. So the two systems sit there, both accurate, both missing the same thing, and the answer comes from phoning a supervisor. Run the 2 a.m. test on your own plant this week You can measure this yourself in about an hour. No project, no vendor. Pick one bad hour from last month. Not the worst ever. A normal bad hour. Set a timer. Using only your systems, no phone calls and no hallway conversations, reconstruct it: what stopped, when, what was running, which order it was against, what it cost, and what the crew did. Every time you have to ask a person, write down their name and what only they knew. Look at that list of names and ask what happens to that hour if any one of them is on vacation. Then ask what happens if they retired in April. Pull last month’s stop reasons and count the distribution. If most of them sit in two or three generic codes, the field is being used to close a dialog box rather than to record what happened. The output is not a score. It is a list of names and a list of missing facts, and it tells you whether you need new systems or better record keeping. Usually it is the second one, and the second one is cheaper to fix. The quality manager got her answer because a supervisor picked up the phone on a Saturday. That is not a system. That is a favour, and the people who do those favours eventually retire. Count the people in your building who could reconstruct last month’s worst night from memory. In most plants it is three or four. Then look at how many of them will still be there in five years, and decide whether that is a plan.