[Rafal Lukawiecki]

I am not familiar with Arista films, but how you agitate in the tray, and how you agitate in the tank—depending how long the development stage is—can have a major impact on your results, especially with short durations. Rapid inversions of the tank are pretty intense, and if all you did was a gentle rocking of the tray, then I'd say you would have a reason for the difference, especially if the overall dev time was as short as 4-5 min. With 7 minutes, I would think this would amount to something like a 1 min relative difference. Would that matter? If you were constantly leafing through the sheets in the tray, on the other hand, it would give a similar agitation to the tank.

Was the number of sheets you processed, and the quantity of developer used, and the temperature, similar in both methods? After you dissect the issues, perhaps have another go, if you wish to do trays, to make sure it was not just a fluke.

Personally, I avoid trays, to which I am a relative newcomer, because I do not trust myself not to scratch my sheets, while CombiPlan has served me well for 12 years. I use trays for tests, seconds, or negatives that I can easily retake, if I do not have a full batch waiting. In both cases, however, I get similar results, with similar development times, although I have only calibrated for CombiPlan.

PS. Nothing beats doing a film developing time test and getting your own, reliable time. But that is another can of fun.