There are so many Otis Kings Calculator offered on Ebay these days. The question is, Which one is good enough to collect? At what price?

Basically, there are five types of Otis Kings Calculator:

1. Type D, The oldest version. Manufactured around 1921, Characteristic  :  Squared off lower edge on cursor and a triangular-profile top cap. Address : 44 & 66 Bray's Lane Coventry or Ashdene Emscote Road Stoke Coventry or the later production 51 Holborn Viaduct London EC1).
2. Type A, Manufactured around 1923.  Without letters on serial numbers or some with letter 'A'. The early units have key chains loop on top cap and usually nickel plated. The units marked with the Holborn Viaduct address but do not say 'Made in England' anywehre..
3.  Type B. Manufactured around 1930's to Mid 50's. The defining characteristics of this type is the screw that holds the two cursor together, On most, the 'Made in England'  marked on the top cap. The address of Hollborn Viaduct or 171 Seymour Place London. Type B units typically found for serial numbers with letter starting C to R & some S-T, and maybe some of few early model A-B.
4. Type B/C (Hybrid) is a very interesting variant of Otis Kings. It still carries typical characteristics of Type B's: 'Made in England' marked found on top cap and serial number on bottom cap.  Otherwise It looks Exactly like and with the address of Type C.  You will be lucky to find one as not many are out there, manufactured only during transition from type B to C.
5. Type C is the most common otis kings, manufactured from mid 50's to around 1971. Marked with the address of 54 Dundonald Rd, London. Type C units typically found for serial numbers with letter starting from S - Z and the repeating  A & B.

Additionaly, an otis kings can also be differentiated from its scales.Model  K : 414/423, Model L : 429/430 & 416/417 on the old ones, and the rarest Model N 424/422 

I consider my self lucky to have an old type A and one type B/C hybrid Otis Kings in my calculators collection. I hope you'll find this guide helpful. Feel free to contact me if you need more photos and information like the manufacturing date table and serial numbers.

Photos:

1. Type A, older Type B and Type B/C hybrid
2. Type A
3. Type B/C hybrid
4. Type C