The length, breadth and height of a box is 506 cm, 345 cm and 253 cm respectively.  Give the length of the longest scale, so that the three dimensions of the box can be measured?

23 cm

506     345     253

  ↓       ↓  ↓      ↓

     ↓           ↓

   161 ....   94 ..... (differences)

 23 × 7      23 × 4 

So, the length of the longest scale is 23 cm