With 'Measure Random' you can place blocks on linear entities like the measure command. However with 'Measure Random' the distance between the blocks is random. By default the min & max method will be used. This means the command will be pick a distance between the minimum and maximum you specify. You can also add an increment to have a bit more control on the distances. Or you can use the list method. In that case you can create a list of distances you want to apply. Between every block the command will randomly pick one of those distances. With the placement option you can determine how the blocks should be placed. By default the blocks will be placed around the geometric midpoint of the linear entity. That means the distance that is left at the start and end point of the linear entity will be equal. You can also choose to place the blocks from the start or end of the linear entity.