5.4.7 Alignment (equalisation below) Analogue equipment requires regular alignment to ensure that it continues to operate within specification. It is recommended that heads and tape path be thoroughly cleaned every 4 hours of operation, or more frequently if required, using a suitable cleaning fluid such as isopropyl alcohol on all metal parts. Rubber pinch rollers should be cleaned with dry cotton buds or with cotton buds dampened with water as necessary. The older, original rubber pinch rollers can gradually become brittle if cleaned with alcohol, increasing wow and flutter. The new generation of polyurethane pinch rollers, generally coloured dark green, may dissolve if cleaned with alcohol. Heads and tape path to be demagnetised every 8 hours of operation, tape path and replay characteristics checked for alignment every 30 hours of use and equipment should receive a total alignment and check every 6 months. In the same way that machines and tape are going out of production, suitable test tapes are likewise becoming difficult to obtain, and some are now unobtainable. It behoves the archivist to acquire enough open reel and cassette test tapes to manage the transfer of their collection.