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Spectrum advice: Numbering

This Spectrum advice fact sheet gives guidance on numbering your collection, on different types and number formats and a summary of commonly occurring issues surrounding numbering. It was revised in 2015 to support the requirements of the Accreditation Scheme for Museums and Galleries in the UK and updated in 2018 for Spectrum 5.0.

  • What is meant by ‘numbering’?
  • Spectrum 5.0 and Museum Accreditation
  • Why is numbering important?
  • Different types of numbering
  • External numbering systems
  • Numbering archaeology
  • MDA codes
  • Re-numbering
What is meant by numbering?

‘Numbering’ refers to the allocation of a unique number to a single museum object, or group of objects. The number is physically attached to the object, or group, and also appears on records which relate to the object, or group. Most museums will need to use several distinct numbering sequences for different procedures within their documentation system. The sequences needed and the form numbers take will vary from museum to museum depending on individual needs and past practice. Museum object numbers are codes for identification and cross-referral. They should not include catalogue information such as classification/subject codes or storage locations.

Spectrum 5.0 and the Museum Accreditation Scheme

It is a requirement of the Museum Accreditation Scheme that the Spectrum ‘Primary Procedures’ are in place in Accredited museums – see Accreditation Standard, Requirement 2.7. Spectrum primary procedures are the foundation of a basic museum documentation system. Numbering systems are used in all of the primary procedures and you will need to record top level policy decisions about your numbering systems in your documentation policy. Museum Accreditation also requires that a museum has a documentation procedural manual in place, which reflects how your museum applies the primary procedures. You will need to record your museum’s numbering systems and how they are used in your procedural manual. For more about procedural manuals and their contents, see the procedural manual template.

Why is numbering important?

Numbering museum objects is important because a unique number, once allocated and physically attached to the museum object, creates a link between that object and its associated information. If the link is broken, for example because the number has fallen off the object, the link between the object and its information is lost. This means that the museum no longer knows what the object is, where it is, or how it was acquired, and will have to spend valuable time and resources re-establishing the link between object and information in a backlog or retrospective documentation procedure.

Accession numbers are attached to objects using standard labelling and marking techniques. See the popular resources panel for useful resources on labelling and marking museum objects.

Different types of numbering

Entry numbering

Entry numbers are used during the Spectrum Object entry procedure and Loans in (borrowing objects) procedure. The entry number provides an initial unique number for every object or group of objects entering the museum – it is the number allocated on the entry form, and it is always attached (usually written on a label and tied) to the object when it enters the museum. It identifies objects until they are either returned to their owner or formally acquired by the museum. If it is not possible to number every object in a group, assign numbers to groups of objects, and record the number of objects in the group on the entry form.

Entry numbers are allocated by taking the next number in the sequence being used by the museum; they may be pre-printed on the entry form.

What format should the entry number take?

A simple running number sequence is best, usually prefixed with an ‘E’ to distinguish it from other numbering systems:
eg E2561; E2562; E2563; E2564; E2565
Individual objects within a group can be identified by adding a suffix to the entry number:
eg E2561.1; E2461.2; E2561.3; E2561.4

Accession numbering

Accession numbers are used during the Acquisition procedure and when tackling backlogs using the Inventory procedure. The accession number is the unique number allocated in the accession register and is only applied to objects formally acquired by the museum for the long term collections. Accession numbers are allocated by taking the next number in the sequence being used by the museum. They are always physically attached to, or associated with, the object using standard labelling and marking techniques.

What format should the accession number take?

There are two common approaches:
A simple running number system:
eg 14603; 14604; 14605; 14606; 14607
A more common system is to use the year of accession followed by a running number:
eg 1991.3; 1991.4; 1991.5; 1991.6; 1991.7

If an acquisition consists of several parts, a further suffix can be added to create a unique number
for each part:
eg 1991.24.1; 1991.24.2; 1991.24.3; and 1991.24.4 denotes the 24th accession in 1991, which consists of four parts.

When deciding on your museum’s accession number format:

  • Do not abbreviate the year to just two digits, as hopefully most museums will survive for more than a century. It can also cause confusion, for example, does ‘64.68’ mean 1964 or 1968?
  • Do not place the year element last as this will cause a problem for computerised sorting of records. 1991.5 is correct rather than 91.5 or 5.1991 or 5.91.
  • Do not use the entry number as an accession number, as it will lead to gaps in the accession number sequence when loans and identifications are returned – every object which enters the museum is not destined to become part of the long term collections.
  • Do not preface the object number with a ‘0’. 1991.5 is correct rather than 1991.05.

Numbering single objects and groups of objects

Objects acquired by the museum from different sources should be given separate unique accession numbers. For example, 4 objects acquired from different sources in 1991, would be numbered: 1999.1; 1999.2; 1999.3; 1999.4.

If a group of objects is acquired from a single source, some museums would give a different number to each individual object in the group. For example the group consisted of a collection of four glass negatives from a single source, each could be allocated a separate accession number as follows: 1999.21; 1999.22; 1999.23; 1999.24.

However, this approach can break down if your museum receives a very large collection from a single source, for example if the group consisted of two thousand glass plate negatives. In this case, if you give each negative a separate accession number, you will be unable to allocate new accession numbers until the large collection has been fully numbered and this will probably cause an accession backlog. In this
example it would be preferable to allocate and attach a single accession number followed by part numbers to each object eg 1991. 21. 1; 1991.21.2….to….1991.21.1999; 1991.21.2000. In this case bulk accessioning may also be a possibility.

Transfer of title numbering 

Transfer of title numbers are used during the Acquisition and accessioning procedure. They are the numbers on the transfer of title form, which records the transfer of legal title of the object to the museum. Transfer of title numbers can be a simple running sequence prefixed by a ‘T’ and are not attached to the object.

Exit numbering 

Exit numbers are used during the Object exit procedure. They are the numbers on the exit form, which is used when objects leave the museum as, for example, loans out, transfers or disposals. Exit numbers can be a simple running sequence prefixed with a X. and are not attached to the object.

Temporary numbering 

Temporary numbers are allocated to objects when dealing with backlogs during the Inventory procedure. They are usually a running sequence of numbers, usually prefixed by a letter to denote that they are backlog and temporary eg B376; B377; B379…

Temporary numbers are physically attached to the object, and recorded on a temporary record. If, during the Inventory procedure it is discovered that the object has already been accessioned, the temporary number is removed, and the original accession number is applied. If it is discovered that the object has never been accessioned, and a decision is made to add it to the long term collections, the next number in the accession number sequence is applied and the temporary number removed.

Photograph numbering 

Photograph numbers are the number given to an image, such as a print, slide, negative, or digital image, resulting from the photography of a museum object during collections management activity for example acquisition, conservation, exhibition or condition checking. Photograph numbers are often dictated by the format of the photograph and the way they are stored.

Photographs taken for collections management purposes should not be confused with original images which form part of the long term collections. The latter are always numbered with accession numbers which provide the link between the object, its documentation and any associated collections management images.

Conservation numbering 

Conservation numbers are allocated when an object is conserved. If your museum deals with several conservation agencies, you can prefix the allocated number with an institution code to avoid any risk of duplication.

External numbering systems

Some objects or groups of objects may have pre-existing numbers, for example:

  • A collection from a private collector, may carry the collector’s numbering system
  • Objects that have been included in a special exhibition may be associated with special catalogue numbers

External numbers should be recorded in the catalogue record for the object, even though the museum’s own numbers will be used as the reference for the object, and applied to the object.

Numbering archaeology

There are two options for assigning accession numbers for archaeology:

  • Use a museum accession number, which is given to the site excavator

This is frequently the best option for long-term curation, as it will fit in with existing museum systems and it means you will not have to re-mark objects. This may be the preferred method for museums which regularly receive archaeological archives from a number of different sources.

  • Use the excavator’s site code

The site code can be incorporated into the accession number. However, as site codes tend to be alphanumeric you will need to ensure that that your information systems can logically handle these codes. A site code usually includes the location and date of the excavation.

MDA codes

As many museums use similar numbering systems the Collections Trust can issue your museum with a five-letter MDA Code, which will uniquely identify an object to its museum within the UK. In the following example the MDA code ‘CAMCD’ prefixes the accession number:
CAMCD : 1991.24.1; CAMDC 1991.24.2; CAMDC 1991.24.3 and so on.

The MDA Code identifies which museum an object belongs to and should be marked on all objects with the accession number whenever possible. However, some objects are too small and can only be marked with the accession number.

You can find out more about MDA codes and how to get one for your organisation by following this link.


Many museums have old numbering systems which do not meet the standards in this fact sheet. When this happens re-numbering collections is often suggested, particularly when ‘intelligent’ accession numbers have been used which have ceased to be meaningful, for example a classification code which is no longer in use has been included in the accession number. Re-numbering is also sometimes suggested when there are gaps in accession number sequences.

As a general rule however, re-numbering a collection is not worth the time and effort involved. It is better to start a new numbering system for new acquisitions and work with existing systems for objects that have already been numbered. At its most basic a numbering system should simply aim to provide a unique number for each object. This number will link the object to the information held about it. If the object can be identified and the accompanying information can be found, it doesn’t matter if the numbers don’t run in sequence or have different forms. Any decisions about formats will need to be recorded in your documentation procedural manual.

For more advice about re-numbering, please follow this link.

Date created: 2015

Publisher: Collections Trust