TouchUV problem

I am using the llDetectTouchUV(0) on a simple object and am puzzled by the results.
If I create a simple square box 4m x 4m x 0.2m and embed the script:

default
{
touch_start(integer total_number)
{
vector UV = llDetectedTouchUV(0);
float U = UV.x;
float V = UV.y;
llOwnerSay("U: " + (string)U + " V: " + (string)V);
}
}

then touch the box in the SW corner of the top face I get values close to 0.0 for U and V, and appropriately if I touch the NE corner values close to 1.0.
If I then apply a texture to the top face I get similar results but if I change the repeats per face in the horizontal direction U to say 0.5 the SW corner gives me a U value of about 0.25.
Is the texture what is being tested or the face?

If you use llDetectedTouchUV, you are detecting position on the texture. If you use llDetectedTouchST, you are detecting position on the face.

OK Thanks. I promise to read more fully the text describing the different commands.