Abstract: A method of selectively displaying data, whereby the data is arranged in a consecutive series of data-blocks, each data-block being a matrix of information such as a Lofargram. The method comprises selecting an initial set of data-blocks from the series of data-blocks, wherein the initial set of data-blocks comprises an initial data-block and every following nth data-block in the series and then displaying this initial set. The method includes displaying different sets of data-blocks subsequent to the initial set. Each different set of data-blocks comprises an initial data-block, differing from the initial data-block of the preceeding set by an integer m, and every subsequent nth data-block in the series. The method further comprises, displaying a reference data-block adjacent to any one of the sets of data-blocks for comparing with any one of the data-blocks in the series.