Branded on front but no discernable model no. but part of obsolete 1-18 range of model no.'s abandoned circa 1930 + cm scale in well of stock + metal backing plate & paper table of conversion factors/scale on bac

Part of obsolete 1-18 range of model no.'s abandoned circa 1930 + metal backing plate & paper table of conversion factors/scale on back

Classroom version for models 40RK & 43A - Sun was added later as company logo ​

Branded in well but no discernable model no. + unusually extra S,T scales on the bottom side edge + metal backing plate & plastic table of conversion factors on back

metal backing plate

unusually extra S,T scales on the bottom side edge + metal backing plate & plastic table of conversion factors on back

branding on back of stock + A model no. suffix = additional catalogue/bookkeeping listing but otherwise no change to 149   

For Electrical Engineering + D model no. suffix = with DI scale but otherwise replaced 155 + metal end braces

model name suffix L probably refers to the LM scale for calculating Logarithmic Mean Temperature that replaced the F(t) scale found on the original 257 + special gauge marks for determining atomic & molecular weights    

branding on back of stock + metal end braces + D model no. suffix = with DI scale but otherwise identical to 259

metal end braces + WULFF & UNIVERSITY with branding stamped into both side edge

Reissued version of model 50W for post 1940 2600 series with the K scale unusually delegated to back of slide + metal backing plate & plastic table of conversion factors on back

Cobranded with Masoneilan + S model no. suffix possibly = 2664 with supplementary green coloured CIF scale + metal backing plate & plastic table of conversion factors on back

metal backing plate & plastic table of conversion factors on back

Desktop version of 25cm model 255 - ​§ scales on front face for converting degrees into radians & vice-versa - supposedly for Advanced Electrical Engineers.

metal end braces - desktop version of 259​

Promotional model for Swedish company + metal backing plate

Metal backing plate

Design invented by Prof. Keisuke Izawa of Tokyo Institute of Technology for frequency responses of physical systems where transfer functions can be linear & exponential + extremely complicated to use with multiple cursors + metal backing plate + see also advanced sibling 301A 

Designed  by Prof. Keisuke Izawa of Tokyo Institute of Technology for frequency responses of physical systems where transfer functions can be linear & exponential + overlay co-developed with Tomoaki Morinaga especially for quadratic factor + extremely complicated to use with multiple cursors/overlay +  metal backing plate + see also “basic” sibling 301 

Identical to model 30 but given model no. 32 because of magnifying cursor + red logo on right-hand end of slide = retailer's trademark + metal backing plate

Model no. suffix R = with reciprocal CI scale (suffix later dropped) + co-branded on back POST 1441 + metal backing plate

metal backing plate stamped with “G. DIKKES & Co N.V.”

significance of the P model no suffix not known + metal backing plate stamped with “BYGGNADS AB JOHAN GUSTAFON & SONER”

branded on front but no discernable model no. + R model no. suffix = basic 34 with reciprocal CI scale + metal backing plate

RK model no. suffix = basic 34 with reciprocal CI & K scale + metal backing plate

T model no. suffix possibly = basic 34 with Trig scales + metal backing plate stamped with “SUN”

T model no. suffix possibly = basic 34 with Trig scales + plain (no SUN or ASEA stamping) metal backing plate

metal backing plate stamped BOFORS

branded on front face  but no discernable model no. + metal backing plate & plastic table of conversion factors on back

RK model no. suffix = basic 40 with reciprocal CI & K scale + metal backing plate

same as 4x models but with an extra CI scale + metal backing plate

/3 model no. suffix = 3-line cursor + later siblings

Wider version of 64T Extended Rietz + T model no. suffix possibly = basic 64 with extra Trig scales + cobranded Dutch retailer Ahrend on front face + table of constants & green pads on back + earlier thinner 64T sibling - also sold as Ahrend 643T

considered extended version of the basic Rietz 64 because of additional scales + T model no. suffix possibly = basic 64 with extra Trig scales + later broader 642T sibling + metal backing plate & plastic table of conversion factors on back

Branded in well but no discernable model no. + table of conversion factors on back - also sold as Tamaya 4480 

branding on back of stock + metal backing plate

Considered an improved layout because of extra peripheral hairlines on cursor + metal backing plate + Dutch retailer Ahrend printed on back

branded in well but no discernable model no. + W,V scales in well + /1 model no. suffix = 1-line cursor + metal backing plate

branded in well but no discernable model no. + W,V scales in well + /3 model no. suffix = 3-line cursor + metal backing plate & plastic table of conversion factors on back

branded in well but no discernable model no. + W,V scales in well + /3 model no. suffix = 3-line cursor + metal backing plate & plastic table of conversion factors on back

Probably a promotional give away for a professional baseball team but model is listed in Hemmi Catalogue 6911 + example calculations in instructions use baseball data from 1965 season

Maker's branding only stamped into cursor + 3rd party dual branding with econosto n.v. + green end braces & Reynolds No. on back +  

P model no. prefix = plastic + green coloured end braces

Plastic version of 264 marketed with an "Arrow Feather Shape" for easy/smooth operation + grey end braces on back

Green end braces & cursor trim

Dark-grey end braces with cursor windows

P model no. prefix = plastic & K model no. suffix = addition of K scale to basic 45 but other than being  open-frame, identical to 45K + green coloured end braces

All plastic version of 45K + /S model no. suffix = simplified version of P45K