Test strips
 

The normal means of making test strips is used where an exposure of say 5 seconds is repeated progressively across the paper by blocking the light to certain parts with an opaque card. To gain an accurate insight into the correct exposure it helps to use large pieces of paper rather than thin strips. As you need to see the full range of potential exposures across as many tonal areas as possible it helps to run the test through these areas as in the case of the illustration where the sky, ocean and land appear in each exposure test.

If the test exposure were run across the would not show the sky as one exposure the ocean as another etc.