The gemara says we paskin like Rav Papa and Rav Huna brei d’Rav Yehoshua. It is unclear whether we are paskin like the first version where they did like Rav Nachman or like the second version where they did not. It is also unclear which version of the sixty times we do (as per the machlokes amoraim on 58B)
The Nimukei Yosef rounds up these two issues, saying that we paskin like the first version where they did like Rav Nachman said, and the way we determine the damage is by taking sixty similar date palms and seeing how significant the devaluation of this one is from that perspective.
As an aside, it is interesting to note that we take a multiplicative factor of sixty, in effect nullifying the damage (בטל בששים)! This needs explanation.