The horizons are not uniformly or continuously stratified. From the basement to the youngest layer, the sequence varies from place to place and I’m supposed to grid these horizons but first have to create isochrons of the horizons. I could have from the basement, uniformly overlain to layer 10 or 9 and above that the presence of the others varies from place to place. Do I have to deduce the stratigraphy from place and use the “Extended Math Calculator” for each? I will need a composite output so in that case, how do I do this if it is the way to go? Some direction to a tutorial on how to use “Extended Math Calculator” would be very much appreciated.