Question Beuchat Espadon Sport 16mm Band length

[Kartonschachtel]

Hi,
I recently went into to store to buy some new rubberbands. They guy gave me 22cm bands for the 90cm speargun. But it seems awfully short to me. Can anyone tell me the real length I should buy?
Thanks

 

[rollerGR]

Measure distance from where the rubber starts at the muzzle down to the last notch (or shark fin), subtract the wishbone's length and any band that isn't getting stretched, and divide what you get by 3 or 3,3 or 3,5. For 16mm probably go with something close to 3,5