The full, half, and quarter straights in this system are all multiples of 90mm in length.  However, sometimes, especially when building complex layouts, you need some short, odd-length straight sections to complete the track by filling in a gap to allow that last track connection to be made.  One or more of these sections, alone or in combination with half or quarter straights, will allow you to make up any length you need to close the gap.  This makes the SCX digital track system more versatile and space efficient while greatly expanding your options for layout design.