What is an Alibi memory?
The Alibi memory is a tamper-proof store in the scale terminal in which every legal-for-trade weighing is recorded: weight value, time stamp and a unique, sequential Alibi number. The store is part of the verified system – its entries can neither be changed nor deleted afterwards. Historically the print strip at the weighbridge cabin played this role; the Alibi memory is its digital successor. Crucially: the entry in the Alibi memory is the legally authoritative original of the measurement. Everything that comes after it – database, weighing ticket, ERP posting – is a copy.
Why the software must reference the Alibi number
A connected PC or server application is usually not part of the verified system. The weight value in your database could therefore, in theory, have been altered – on its own it has no evidential value. It only becomes reliable through the link to the unchangeable original: if the Alibi number is on the weighing ticket, any value can be checked against the entry in the terminal at any time. This is why legal-for-trade weighing software must ensure:
- The Alibi number is captured from the terminal automatically at every weighing – never entered by hand.
- It is stored unchanged together with weight and time stamp and shown on every document (weighing ticket, invoice).
- Weighings without a valid Alibi number are flagged as such or rejected.
Typical implementation in practice
The usual sequence: the software requests a registered weighing from the scale terminal. The terminal waits for a stable reading, records the value in the Alibi memory and returns weight, time stamp and Alibi number as a data record. The software stores this triple, links it to the business transaction (vehicle, order, batch) and generates the weighing ticket and posting from it. How the request works technically differs by manufacturer and terminal – but via RS232, TCP/IP or OPC UA the mechanism is available on most common devices.
Frequently asked questions
What is an Alibi memory on a scale?
An Alibi memory is a tamper-proof store in the scale terminal in which every legal-for-trade weighing is recorded with a unique, sequential Alibi number – together with the weight value and a time stamp. It is part of the verified system and cannot be altered afterwards. It thus replaces the paper print strip once common: the value stored in the Alibi memory is the legally authoritative original of the measurement.
Why does my weighing software have to store the Alibi number?
Because the software itself is usually not part of the verified system. The value in your database, on the weighing ticket or on the invoice only holds up legally if it can be linked to the tamper-proof original in the Alibi memory – and that is exactly what the Alibi number provides. Good weighing software therefore captures it automatically from the terminal at every weighing and prints it on every document.
Software for legal-for-trade weighing
Digital Trend Systems builds custom weighing software that requests, stores and shows Alibi numbers correctly on every document – vendor-independent and matched to your terminal. Whether your application is subject to mandatory verification at all is covered in our guide Verification or calibration.
Related topics
