These cards have microfilm inserts of original Department of Works drawings registered during the period ?1945-1958 and are related to all disciplines involved in the construction or maintenance of buildings and projects owned or operated by the Commonwealth Government.

Two 'masters' are produced, one of which is held by the controlling agency and used as an index. Reproductions can be made from this set which is held by the agency, on an as required basis, a cheaper method of reproduction is used to obtain the copy, which is termed a Diazocopy. The aperture cards supersede the former half-plate negative method of reproduction which was in use from 1959-1972?, records which had already been reduced to half plate negative size have undergone further reduction to 35 mm aperture cards. So that, there are in existence concurrently, the original tracings, the half plate negative, and the aperture cards of a given drawing. Microfilming is carried out retrospectively.

Also because of this reproduction process, the researcher will find that the informational content of the cards, precates the existence of micrographics as a records keeping aid in this area of Government administration. After microfilming that portion of the original plans and drawings series assessed as having permanent value is transferred to archival custody. The transparencies 44 x 30 mm in size are contained within and form part of the aperture card, which has an overall measurement of 187 x 83 mm.

The cards show the following information: the registration number, with regional and discipline prefix; eg WC 121, the 'W' indicates the Western Australian region, the 'C' is an indication that the discipline involved is Civil Engineering and the number is the consecutive registration, the sites or location of the job is to be found in the top left hand corner of the card, the job details in the transparency. The agency no longer use this method of registration of the original plans and drawings, a new system was introduced on the 1st January 1959. Region: "W" - Western Australia. Discipline symbols are as follows and are usually the second letter in the prefix : A - Architectural, B - Civil Engineering, S - Structural, E - Electrical, M - Mechanical, H - Hydraulic.

These aperture cards were not produced until 1978, microfilming by the agency in the WA region did not commence until 1977, prior to this records were sent to the Central Office of the Department for filming.