Comparing

famulus-astra diff <a> <b> compares two texts of one kind. The output states; it does not interpret.

Two models: identity

First whether the two are the same geometry up to renaming — a structural signature: every object as its expression with the names replaced by their kinds — then what one construction has that the other lacks.

$ famulus-astra diff solar-eccentric solar-epicyclic
solar-eccentric ↔ solar-epicyclic: different geometries
  parameters
    − R
    − e
    + R'
    + r
  construction
    − E (point) = O + polar(e, lamA)
    − ecc (circle) = circle(E, R)
    …
    + def (circle) = circle(O, R')
    + C (point) = O + polar(R', lamA + kappa_bar)
    …
  shared construction: O

That two different models nevertheless agree in where the sun is, or in where it is seen, is not something diff can say. It is an equivalence: the conclusion of a derivation in their superposition (Superposition, Derivations).

Two parametrisations: the values

$ famulus-astra diff solar-eccentric.ptolemy solar-eccentric.battani
solar-eccentric.ptolemy ↔ solar-eccentric.battani
  values of Ptolemy ↔ al-Battānī
    R: 60 ↔ 60   (equal)
    e: 2;30 ↔ 2;4,45   (−0;25,15)
    lamA: 65;30° ↔ 82;17°   (+16;47)
    T: 365;14,48 ↔ —
    kappa_0: 0° ↔ —

One model, two parametrisations, symbol by symbol. This is the comparison that the page’s sentence on al-Battānī makes in prose.