In college I created my own harmony of the Synoptic Gospels to try to discern the relationships between them. It can be found here in my OneDrive account. It is color-coded and in chronological order. The significance of the colors is as follows: Black: all three gospels; Green: Matthew only; Orange: Mark only; Blue: Luke only; Red: Matthew and Luke; Pink: Matthew and Mark; Brown: Mark and Luke. Based on the fact that only the four stories of the parable of the growing seed, the healing of a deaf man, the Bethsaida blind man, and the account of the young man fleeing are found in Mark alone, I concluded that Mark was written first and Matthew and Luke both used Mark as a source for their gospels.