Datasheet legend
Ab/c: Fractions calculation
AC: Alternating current
BaseN: Number base calculations
Card: Magnetic card storage
Cmem: Continuous memory
Cond: Conditional execution
Const: Scientific constants
Cplx: Complex number arithmetic
DC: Direct current
Eqlib: Equation library
Exp: Exponential/logarithmic functions
Fin: Financial functions
Grph: Graphing capability
Hyp: Hyperbolic functions
Ind: Indirect addressing
Intg: Numerical integration
Jump: Unconditional jump (GOTO)
Lbl: Program labels
LCD: Liquid Crystal Display
LED: Light-Emitting Diode
Li-ion: Lithium-ion rechargeable battery
Lreg: Linear regression (2-variable statistics)
mA: Milliamperes of current
Mtrx: Matrix support
NiCd: Nickel-Cadmium rechargeable battery
NiMH: Nickel-metal-hydrite rechargeable battery
Prnt: Printer
RTC: Real-time clock
Sdev: Standard deviation (1-variable statistics)
Solv: Equation solver
Subr: Subroutine call capability
Symb: Symbolic computing
Tape: Magnetic tape storage
Trig: Trigonometric functions
Units: Unit conversions
VAC: Volts AC
VDC: Volts DC
Years of production: ~1900 Display type: Analog slide
New price:  
Display color: N/A
    Display technology: Mechanical
Size: 4"×2½"×½" Display size: 2½"
Weight: 3 oz
    Entry method: Analog slide
Batteries: N/A Advanced functions: N/A
External power: N/A
Memory functions: N/A
I/O: N/A    
    Programming model: Slide rule
Precision: 3 digits Program functions: N/A
Memories: N/A
Program display: N/A
Program memory: N/A
Program editing: N/A
Chipset:   Forensic result:  

swatch.jpg (15796 bytes)Call it an exercise in elegance.

This pocket watch-like device is a circular slide rule calculator with five scales. In expert hands, it can be used to quickly compute powers, logarithms, and trigonometric functions to 3 digits of precision. Its small size and compact shape probably made it a desirable item to carry by many engineers, even though its limited precision was not sufficient for more elaborate computations.

The device has five scales, that can only be moved together by rotating the large knob. The scales cannot be moved independently of each other (they're on a single sheet of cardboard paper that serves as the watch's "face".) This shortcoming is alleviated by the fact that the device has two pointers; one is fixed as the 12 o'clock position, while the other can be rotated using the second knob.

The innermost scale is marked in degrees from 0º to 90º. The outermost scale, with values from 0 to 1, is the sine of the values on the innermost scale. I.e., labeling the scales with the letters $A$ through $E$ starting from the inside, $E=\sin A$. Scale $D$ is the power-of-ten of the value of scale $E$: $D=10^E$. Scale $B$ is the square root of scale $D$. Lastly, the values on scale $C$ are the values on scale $B$ multiplied by the square root of 10.

I am no slide rule expert, but I do believe that these scales are somewhat unorthodox. Nevertheless, it appears that they are quite sufficient for many typical engineering computational tasks. Together with a mechanical digital calculator like a Curta, an expert user could accomplish many of the same computational tasks as with today's scientific calculators, almost as easily, almost at the same speed, although with a significantly lesser precision.