Ilford MGRC V Deluxe exhibits a little reciprocity error. Upper patch was exposed for 32 times as long as the row beneath it. It should have matched patch on far left. This experiment shows that doubling exposure-time causes a 1/50th stop loss of density due to reciprocity-failure.
Fascinating.
I notice reciprocity on my darkroom paper (Ilford Cooltone RC) - but never thought to test it in such a scientific manner.
Obviously the new MGV is much better at managing the phenomenon.
Martin