Find the cross-strata dip,
given two of its trend+plunges

Enter values, then press

Azimuth difference (btwn trends)
Plunge1 (ie., dip) of one lineation
Plunge2 of other lineation

The trend+plunge pair come from two lineations. Works, of course, only if the cross-strata are planar. If the cross-strata are parallel, the lineations can come from adjacent strata.

Spreadsheet version (eg., for phone)