Abstract: An abradable liner for a gas turbine engine compressor stage, comprising: an abradable body having a radially inner surface over which an aerofoil tip passes in use; a plurality abradable depth indicators extending into the body from the surface; each depth indicator may be filled with a visual indicator. The depth indicator can be observed by a boroscope to provide a simple mechanical visual indication which can be used to provide quick and reliable information as to the extent and pattern of wear in an attrition liner.