Enterprex SR-815

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Calculators: Handheld: Enterprex SR-815 (aka Slide Rule) (possibly branded Victron SR-815)

		Size (approx):	80mm x 135mm x 22-40mm (w,h,d) Weight 160g excluding batteries
		Power:	6.0V DC, 4 x AA size batteries. It accepts an adapter/charger (6V DC, 0.35W) through a socket on the top side to the far right.
		Case:	Heavily wedged shaped case made from two pieces of smooth grey plastic. The top area has a metallic sticker printed red and black with the brand name and model in its own bordered section. Below this is a green plastic display filter that is inset and tilted. This gives a large and bright image. The matt black plastic keyboard surround has raised silver printed switch and extra key labels and looks very much like some Commodore keyboards. The small keys are squishy and medium travel.
		Display:	8 digit green VFD with ninth digit for minus sign, error and function indicators
		Features:	Four function with reciprocal, square root, pi, change sign, trigs and logs, register exchange, register recall, powers and four function memory. Switched degree/radian mode.
		Age:	1975
		Manufacturer:	No information. Serial number 12881.
		Comments:	Solid calculator with a lovely large display that has a Commodore-like keyboard surround though it is a little annoying not having the (=) key at the bottom right. The silver painted extra labels have not survived well on my example. The logic is OK, if a little inaccurate with good recovery and only the pseudo fixed decimal bug. This is possibly just a branded version of a Taiwanese calculator Victron.

Components:	1 x cpu: Rockwell A4001PC 7522 (week 22 of 1975) 42 pin staggered DIL, 0.6" width 1 x 9 digit VFD, single tube round face 4 x transistors 6 x diodes 18 x resistors 5 x capacitors 1 x transformer
Boards:	An L-shaped cpu board (VIC-509S) sits loose in the rear of the case and is attached to the keyboard assembly by 13 long wires. The latter is attached to the front by four plastic clips.
Construction:	Remove the two upper rubber feet from the back. You will now have access to the two screws that sit in these holes. The front of the case will then lift off easily, hinging from the bottom.

Logic comments:	(CL) cancels an incorrect numerical entry, pressing a second time clears the calculator
	Input overflow is suppressed, typing in nine digits ignores the ninth
	There is automatic constant on all four functions
	Negative numbers are shown by a minus in the far left (ninth) digit thereby allowing full eight digit negative numbers
	Overflow shows the result and "ⁿ" ("o" if negative) in the far left (ninth) digit and is recoverable using (CL)
	Divide by zero results in zero and "ⁿ" in the far left (ninth) digit and is recoverable using (CL)
	The change sign key can be used in mid entry of a number
	Higher functions are selected by pressing (F) first which causes the decimal point of the far left (ninth) digit to light.
	The (X-Y) key exchanges the current number with the last register
	Negative square roots are not allowed and result in zero with "ⁿ" in the far left (ninth) digit and is not recoverable
	The odd (DR) key recalls the last number entered and is called "register recall" in the manual. Goodness knows why they labelled it DR then
	The power key appears to use logs to calculate the result and hence is not too accurate, try 6³ by keying in (6)(x^y)(3)(=) to give "216.0003". You can also see the intervening natural log of six when you hit the power key.
	Memory store is not indicated - you have to remember it
	The (X-M) key exchanges the memory with the display register
	Memory overflows are stored in memory and easily recoverable using (CL)
	This calculator has the pseudo fixed decimal bug; key in (0)(.)(0)(0)(0)(+)(1)(=) and the answer will be "1.000". This fixed decimal mode remains for addition and subtraction until the result requires more precision or multiply /divide is used.
	A switch allows you to work in degrees or radians

	Unusual for me to include two scans of a manual but this one makes the effort to have a design on the back page as well as the front. Quite large format measuring 118mm by 168mm printed four spot colour with additional half-tone black. It has 40 printed pages in total, the internal ones being black and white only. English language only it is much larger than the calculator. There are extensive specifications, instructions and scientific examples for a wide range of problems - even the admittance of a coil! Excellent! Quotes of note: "Since electric voltage varies in different countries, you must secure the proper adaptor.." "...Insert 4 pieces of nickle [sic] cadmium batteries into the battery compartment." "Deviation: All the above scientific operation [sic] is programmed to one part of [sic] a million". " True value indication with minues [sic] sign at the 9th digit"
The image on the front shows the calculator to be a Victron SR-815. I suspect that this is a re-branded model. Nowhere else in the manual is a brand or manufacturer or country mentioned.		Look at all those function keys - even "1", "5" and "Clear" ! Sorry, that's my natural sarcasm coming out. I love the open hands design though.
The image of the inside (with the front removed) shows the odd staggered pin configuration of the Rockwell IC. Notice how awkward the design looks. As the battery compartment is in the middle the board is L-shaped (going up the left hand side). The display sits on top of the compartment, held in place with a metal bracket on the right hand side. There is also loads of wasted space at the top, which is really only used for the power adapter socket. A large bunch of wires goes of the the right, to the keyboard assembly.