Clarification needed for clues with variation of ‘which itself’

[StumpedDarlin34]

I’ll get right to it.

Clue: $188 siren is rated 5 decibels quieter than Armor-Stop, which itself is rated 5 decibels quieter than the siren released in 1994.

Is the clue saying 1) $188 is ALSO rated 5 decibels less than the 1994 or 2) Armor-Stop is 5 decibels less than 1994.

Is there a general rule that can be applied to clues written this way?

[jezzat]

I would read it as option 2 of the ones you give. If so, "which in turn" might be a better wording than "which itself"

[StumpedDarlin34]

Thank you so much!

[Faymie]

I usually play "challenging," but I've never gotten that kind of clue.

[Faymie]

For what it's worth, I would also interpret it as the second info you spoke of.