ANGLEBETWEENBEARINGS
=LAMBDA(ab,
    DEGREES(
        BEARINGDELTA(
            RADIANS(ab)
        )
    )
)


BEARINGDELTA
=LAMBDA(ab,
    LET(
        sinab, SIN(ab),
        cosab, COS(ab),

        ax, INDEX(sinab, 1),
        bx, INDEX(sinab, 2),
        ay, INDEX(cosab, 1),
        by, INDEX(cosab, 2),

        rem, "Sign * dot product",
        IF(0 < ((ay * bx) - (by * ax)),
            1,
            -1
        ) * ACOS((ax * bx) + (ay * by))
    )
)