larger tanks can process many sheets of film at the same time. Tank processing, like using trays, must also be performed in the dark. Some photographers report uneven development using this method. There are also daylight tanks accepting sheet film, usually adjustable to multiple existing sheet formats - e. g. inch and metric, and allowing the processing the sheet film in daylight. They have to be loaded in the dark, though. The stainless steel Nikor tank accepts up to 12 sheets of film, 4x5" size maximum, and requires about 1 liter of chemistry. These tanks have long been discontinued, and are only available used. Some people report uneven development and emulsion scratching with this device (a result of steel "spider" presence, separating the sheets in tank's "cage" ), but many users get excellent results with it - the right loading and infrequent agitation are perhaps the keys to success. The current make plastic Combi-Plan tank accepts up to 6 sheets of film, and works nicely, though the overall quality of manufacture is not too high, and the tank has a number of small plastic details, easy to break or lose. But this tank is also quite capable of excellent performance. Rotary tube processing With rotary processing, films are loaded into tubes for processing. The solutions are poured or pumped into the tubes, which are turned on their sides and spun, sometimes by hand, and sometimes by a motorized base or machine. The simplest form of rotary processing is to use one tube per film; no extra reel or complex film-holding device is needed. The film is loaded, solution added, tube closed, and the tube is spun, by hand, floating in a water bath. The direction of spin is normally reversed after a couple of spins. Some rotary tubes utilize reels to hold multiple films inside the tube. Some rotary systems use a motor to do the spinning, instead of the photographer. These systems sometimes have variable rotation speeds, and will reverse direction automatically. Systems such as these are quite convenient; they require nothing of the photographer other than changing the solution at the appropriate time. Some more complex systems can even do the chemistry management, requiring nothing but a simple programming step. Benefits of rotary systems are even development, and very low solution requirements in some cases. However, they can also require the use of more chemistry than normally needed