InstrumentThe picture shown to them comprised of three parts: (a, upper part) a set of vectors with arrows, (b, middle part)a side view of two bikers moving in opposite directions and (c, lower part) a definition put in a formula.The material given to the students to solve the problem had been reduced from reality. The drawing provided shows vectors representing the velocity of the wind and the velocity of the rider. The velocity of the rider relative to the air, asevoked through the length of the vector, is the same in both directions. The students had been told that the velocities have to be added to obtain the velocity relative to the air. This should easily evoke the idea that the rider tries to maintain the same velocity relative to the air (not to the ground) in bothdirections. This instrument of dividing the picture into parts can be effective for serving the purpose of this study because the efficient part of the picture can be traced this way.