Notes: "The Hemmi model 255 slide rule is for the “Expert Electrical Engineer”. The main features of that make it specialized for electrical engineers are the three hyperbolic scales, and the trig scales being in radians rather than degrees. The x and ? scales are for conversions between degrees and radians. Other than that, it is a fairly conventional log log duplex slide rule, suitable for most common calculations as well as specialized electrical ones. "
