Suunto computers of that vintage are very conservative especially in repetitive diving and other scenarios specific to these computers. Using both, a Shearwater Terric and a Suunto Cobra, will present a problem to you when one, the Cobra, has much shorter NDL's than the other, the Teric, and you will have to either end the dive or have to do a "required deco stop" when the Teric has plenty of NDL. If you ignore the Cobra and just go by the Teric NDL and exceed the Cobra's NDL and not make deco stops, your Cobra will lockout when you arrive at the surface and it won't go into dive mode for your next dives for 48 hours (as far as I remember) after the last dive. It is very difficult to use a Suunto computer as a backup to a more modern dive computer that uses a less conservative algorithm. If you want to please both computers, then you will need to go by the limits the Cobra gives you and use it as the primary computer and let the Teric be the back up. I don't think that this is a pleasing scenario after you have paid good money for the Teric.