Calculators: Desktop: Anita 1011 LSI
Size (approx): 
223mm x 90mm x 140mm(max)
(w,h,d) 

Power: 
Mains (190235V, 210250V 50/60Hz, 13 Watts, 0.06A) power through a permanently fixed, two wire mains cable of reasonable length. This enters the calculator on the top edge, towards the base and to the left.  
Display:  10 digit nixie tube display with additional neon lights for decimal point, negative and memory indication.  
Features:  Standard four functions with switched constant, percentages and two function memory. RPN logic.  
Age:  1972  
Manufacturer:  Anita. Distributed in the UK by Sumlock Comptometer Ltd., 39 St. James Street, London SW1. Tel 01493 1532. Made in Great Britain. Serial number LM12379. My example also has a sticker on the top edge "Supplied and Serviced by Sumlock Office Services (SOS), 465 Alexandra Avenue, Rayners Lane, Harrow, Middx. HA2 9RY Tel 01429 0747". Also seen LM124917.  
Comments:

Innovative, compact and futuristic design for its day. The RPN logic and some of the memory and percentage functions is not only archaic, but sometimes counterintuitive. As one would expect from this early date, loads of bugs, strange overflow and underflow handling and even stranger divide by zero bug  lovely! 
Case and Design:  Made from three sections of cream and one dark blue smooth plastic. A prominently raised section houses the display tubes at a sharp angle. These are protected by a wraparound orange plastic filter that gives good brightness and contrast. Top left of the keyboard area is a black printed metallic model panel which sits in its own recess.  
Keys and Switches:  Big chunky keys with long travel and a hollow loud clunk and bounce. A simple colour scheme of white blue and red is not too cluttered. The constant key "C" is a rocker switch to match the on/off switch.  
Construction:  From underneath, remove the two screws, turn it the right way up and the upper section will lift off: hinge to the left. 
Boards:  The main board sits face up in the lower case section. The piggyback CPU board (IC board 1230PC iss 8 TA7539 SAE/4/A) sits face down on top of this, connected by pins. A further keyboard board (Keyboard Panel 1206PC iss 10 TA7536) is attached to the front and joined by two power cables and ten wires.  
Components:  A mass of
components including five 12pin roundcan ICs. A row of small
transformers are used to generate the voltages for the Nixie tubes. 10 x Nixie tubes 11 x neon indicator lamps 
Logic comments:  In order to clear the calculator (my example has no zeroonpowerup function), key in (0)(Enter). You can also briefly rock the (C) switch to correct an index error. 
The logic is Reverse Polish Notation (RPN): to do 5x8 key in (5)(Enter)(8)(X) to give "40"  
There is switched automatic constant using (C) on multiply and divide only: key in the number then switch the (C) switch to store as an indexed constant.  
Negative numbers are shown with a minus sign in the far left symbol cluster thereby allowing full ten digit negative numbers  
To use the percentage function you have to operate two keystrokes: 10% of 65 is (6)(5)(Enter)(1)(0)(%)(X)(n), to find out what percentage is 50 of 200 key in (5)(0)(Enter)(2)(0)(0)(/)(n).  
Memory store is by use of the (ENT S) key, but there is no indication of storage. To add to the memory use (STORE)(+) when the "S" symbol lights up in the far left symbol cluster. Do not attempt to accumulate results of overflows and underflows, as it will result in nonsense.  
Divide by zero actually divides by 10!  
Overflow shows the ten most significant digits with the decimal point shifted ten places left. The number of zeros that should follow the displayed digits is the same as the number of digits to the left of the decimal point.  
Underflow shows the ten most significant digits with the decimal point shifted ten places right. The number of zeros that should precede the displayed digits is the same as the number of places to the right of the decimal point: thus "0.02 x 0.003" results in the display "000600000.0" which is "0.00006".  
It suffers the negative zero bug: key in (1)(Enter)(2)() to give minus one, now add one with (1)(+) to give "0" 
Footnotes:  3 June 2011. JW has supplied information about serial number LM107206 but with some doubt about the origin of the mixed collection of boards that came with it. CPU board  IC board 1230PC iss 5 and iss 7 TA7539). Spare keyboard Panel  1206PC iss 7 TA7536. Spare display board 1229PC iss 11. 
10 June 2011. RM has supplied information about serial number LO61050. Display board  IC board 1229PC iss 11 TA7539) Keyboard Panel  1205PC iss 8 TA7536 