In a project that I am carrying out should I count a I number uncertain of heaped slates some above other, do I ignore the sensor type that could use, I have tried to use laser, but is the refraction index very variable, could ultra-sounds be used maybe? some idea? Investimento e Investigacion Industrial, S.L. P.O.BOX 103 32300 Barco de Valdeorras (Orense) Spain TLF. : (+34)909 256412 FAX : (+34)988 300044 E-MAIL: manuel.castro@mx3.redestb.es