Aqueous solutions of inorganic nitrate salts are used to accelerate the gelling of epoxy gelcoat resins without adversely affecting the glass transition temperature of the finally cured gelcoat. By adopting this structure, the tool can be made to behave as a mass-spring structure and its flexural and extensional behaviour controlled such that its dispersion curve does not extend into the dispersion curve of the formation to be logged. The pusher face is transversely extendable relative the track and is extendable from a retracted position to one of several extended positions. The extractor is biased into engagement with the cam, and a second cam follower on the extractor is engageable with the barrel face when the slide moves into battery. With the sensor fully inserted in the pocket, the bottom frame or the bottom edge of the front wall is configured to abut the bottom end of the front side of the sensor, thereby keeping the sensor from inclining backward even if it is pushed backward at its upper portion. The DAX speed for the first audio track is used for recording the first audio track through an audio track immediately preceding the mid-point audio track, and the DAX speed for the mid-point audio track on the source optical media is used for recording the mid-point audio track through a last audio track.