The BTZS Power Dial is a inexpensive but sophisticated device that can help you determine film exposure and development for many popular films under most subject conditions. This novel dial slide rule is constructed of durable laminated card stock to withstand day-to-day use in the field, and is convenient to carry and simple to use.

The ingenious folding slide can be adjusted for use with either the Zone System or the BTZS Incident System and can handle subject ranges of from 4 to 12 stops in either mode. The calculating dial accepts the ISO film speed for the film in use, and works with EV numbers from your meter.

Exposure settings are read directly from the dial, while the subject range in stops and the appropriate developing information (in the form of average gradient numbers) are displayed on the reverse side. This shared development scale avoids the problem of "N-numbers" and provides "stepless" development data in both Zone and Incident modes. Reciprocity compensation data for exposure times of a second or more is provided by two charts one for exposure and one for development on the front of the sleeve.

Intended primarily as a backup for the popular BTZS Expo/Dev for the Palm Pilot, the Power Dial is calibrated to agree very closely with the computer output using an ES value of 1.05, and a flare factor of 0.015. The built-in exposure compensation (for development variations) is suitable for most popular films.

Although it cannot calculate depth of field, closeup compensation, filter factors, etc., and can neither time your long exposures nor record pertinent information about each exposure (as the BTZS computer can), the Power Dial has advantages of its own: it's faster to operate, it's immune to temperature extremes, it's unbreakable, and it doesn't need batteries. In short, the little computer is a more versatile device with many more features, but the Power Dial is an excellent, inexpensive alternative that's easy to use and can solve most of your exposure/development problems quickly and with reasonable accuracy.

Power Dial Features:

• Calculates film exposure settings and appropriate development
• Works with both Zone and BTZS Incident Systems
• Compatible with any meter that can provide EV numbers
• Usefully accurate for most popular films and developers
• Handles an extreme range of subject conditions
• Includes flare and exposure compensation for development variations
• Provides reciprocity compensation recommendations
• Quick and easy to use
• Compact; unbreakable; made of durable laminated card stock
• Immune to temperature variations
• Inexpensive
• Perfect "insurance" backup for your Palm Pilot