AN: Find the differences

Today I've sat in the bench two identical decks to check why one seemed to be faster than the other one.

After doing some electrical measurements, the voltage is more or less the same, even the slowest deck gets more volts in the reel motors and they rotate "without" friction, the same as the other compared deck.

In a first time I thought that there were some electrical problem in the deck, but after doing the measures into the two decks, all doubts were resolved: they both are in good state.

However, one is faster than the other one during RWD and the back tension has been revised.

Do you like to find differences between two images?. Look carefully, they seem identical, but there are differences: