{HEAD ~ a sample holder} guided by said carriage for movement relative to said carriage in a direction perpendicular to the friction surface and said first direction, said sample holder being configured to hold a sample in frictional engagement with the friction surface during relative movement between said carriage and friction surface in said {TAIL ~ first direction} 
{ HEAD ~ a sample holder } guided by said carriage for movement relative to said carriage in a direction perpendicular to the friction surface and said first direction , said sample holder being configured to hold a sample in frictional engagement with the friction surface during relative movement between said carriage and friction surface in said { TAIL ~ first direction }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL