For many years we have used a waterproof observers card which is a carbon type paper in a sealed plastic cover, just write on the plastic and the details appear inside, a none working biro is the best for the job. If it is a wet trial or the plastic gets covered in mud just cut off the plastic covers and you have a nice clean set of sheets to produce results from. We purchase these from Vic Madeley of Mid Wales Trail Riders Association, e-mail vic@mwtra.co.uk, the last 100 we had a few months ago cost in round figures