To record events, a vector A is taken of n measurements An. Each measurement An is converted into a binary vector Bn using a binning process. Measurements in vector Bn, are transformed using a kernel operation, to make a vector Cn. All vectors Cn are concatenated into a single vector D. A binary vector M is created with P bits set. A date and vector A are recorded against vector M in a database Z. Vector D is associated into a correlation matrix memory R against vector M. To recall events, the above steps are repeated up to concatenating all vectors Cn into single vector D. Vector D is then used to access a correlation matrix memory R to recall an association vector S, and vector S is applied directly or indirectly to database Z to recover the or each date associated with vector S. This may facilitate the monitoring of assets such as generators, gas turbines, motors, and larger assets such as trains, boats and planes, to ensure that they continue to operate reliably.