code: @Trivial
      public static String toRelSec(long baseNS, long actualNS, int pad) {
          return toAbsSec(actualNS - baseNS, pad);
      }
docs: Display the difference between two nano-seconds values as a
  decimal seconds value.
  
  Display three places after the decimal point, and left
  the integer value with '0' to a minimum of the specified
  number of characters.
  
  @param baseNS The value to subtract from the second parameter.
  @param actualNS The from which to subtract the first parameter.
  @param pad The number of '0' character to pad to the integer
  part of the value.
  
  @return The value as a seconds value.