This shows the inex and saros numbers for the eclipses of the tetrads between AD 1000 and 2500. A tetrad is a sequence of four total lunar eclipses, separated by six lunar months. The group of four clusters on the right represents the tetrads between AD 1909 and 2156, while the group on the left represents the tetrads between 1305 and 1581. One can see that to go from a clump in the earlier group to the corresponding clump in the group around our time, the saros number goes up by about 19 and the inex goes up by about 2. (Notice that the inex values are higher at the bottom of the graph.) Any eclipse having inex and saros point lying along a line going through the first cluster on the right (at around inex 53 and saros 123) and the third cluster on the left occurs after perihelion and before aphelion (presently Northern Hemisphere spring), whereas any on a line going through the second cluster on the right and the fourth on the left occurs after aphelion and before perihelion (presently Northern Hemisphere autumn).