Elektronika MK-85M

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: 1986  Display type: Alphanumeric display  
New price:   Display color: Black  
    Display technology: Liquid crystal display 
Size: 3"×6½"×½" Display size: 12 characters
Weight: 5 oz    
    Entry method: BASIC expressions 
Batteries: 4×"LR44" button cell Advanced functions: Trig Exp Cmem Snd 
External power: D2-10C adapter   Memory functions:  
    Programming model: BASIC 
Precision: 12 digits Program functions: Jump Cond Subr Lbl Ind  
Memories: 6(0) kilobytes Program display: Text display  
Program memory: 6 kilobytes Program editing: Text editor  
Chipset:   Forensic result:  

mk85m.jpg (30188 bytes)The Elektronika MK-85/MK-85M are described as the last Soviet calculators ever made.

This programmable calculator very closely resembles similar calculators made by Casio. It is programmable in BASIC; the MK-85M provides 6 kilobytes of memory for programs and variables.

Like other Russian calculators that I had the good fortune to explore, the MK-85M is also a very slow device. Programs that execute in a fraction of a second on similar Western devices take several seconds on the MK-85M. However (as it was recently pointed out to me in an e-mail from Aleksandr Abrashkin) the MK-85M has a "fast mode". Holding down the + key while turning the calculator on causes it to run at several times normal speed, albeit at a greatly increased power consumption. Curiously, the same feature is absent in the MK-85M's smaller cousin, the MK-85.

A curious feature of the MK-85M is its ability to address display pixels individually, making it possible to produce some crude graphics. The calculator also has an extensive character set, including both Cyrillic letters (upper- and lowercase) and graphical symbols. Another unusual feature is the undocumented WHO command.

More information about the fascinating history of the MK-85 family is available at http://www.computer-museum.ru/histussr/mk_85_1.htm.

The following implementation of the Gamma function demonstrates programming on the MK-85M:

100 INPUT "X=",X
110 T=1
120 IF X>=0 THEN 160
130 T=T*X
140 X=X+1
150 GOTO 120
160 G=1.00000000019
170 G=G+76.1800917295/(X+1)
180 G=G-86.5053203294/(X+2)
190 G=G+24.0140982408/(X+3)
200 G=G-1.23173957245/(X+4)
210 G=G+1.20865097387E-3/(X+5)
220 G=G-5.39523938495E-6/(X+6)
230 G=LN (SQR (2*π)*G/X)
240 G=G-X-5.5+LN (X+5.5)*(X+.5)