Grey plastic case denotes a later model - “easy reading” blue banding for A/B & C/D scales ​

one open window right with 1 hairline in back - black logo = early model

Does not have cm top edge scale on standard 25cm 1614 ​

Note mixed alphanumeric 16oo model no. - layout different to standard/later 1600 Rietz - black logo = early model​

Ruler with cursor conversion aid + Cicero (old French thumb unit of measure = 27.07mm) is a typographic unit similar to a pica but with 15th century origins​

one open window right with 1 hairline in back

Slightly longer than the 612 - one open window right with 1 hairline in back​

One closed window right with 1 hairline in back​

Model no. on back of slide - one open window with cursor line in back on right​

Two closed windows with cursor line in back + see also smaller 643 sibling

​Late model as colours have sweated or bleed because cheaper methyl ethyl replaced phenol as etching agent - two closed windows with cursor line in back

Missing model no. - table of conversion factor on back + one open window with cursor line in back on right

One open window with 1 hairline ​in back

Name of NL company Ingersoll-Rand in well of stock - one open window right with 1 hairline in back = see also larger 6245 sibling

Unusual inclusion of AI scale ​

§ scales = 2-part COS scale - unusually for Electro’s W & V scales on front face ​

Patented design (CH314378) by Peter Lüthy & Max Nussbaum - § scales for N = 10 - Co. name MONTEFERNO, Bodio (CH) in well & on back - table of constants on back

Patented design (CH314378) by Peter Lüthy & Max Nussbaum - § scales for N = 10 - Co. name MONTEFERNO, Bodio (CH) & table of constants on back

Impressive layout of 25 scales - Neper or Np is a logarithmic unit of measurement of physical field & power quantities + see comparable sibling model 690 a

Impressive layout of 26 scales - Neper or Np is a logarithmic unit of measurement of physical field & power quantities -+ see comparable sibling model 690 - comparable to ARISTO 0968

Same model rebadged for TEXACO & ​CALCRUDE - red outline of logo = early - bizarre cursor design - °F & °C scales in well of stock - back of slide has American Petroleum Institute (API) crude oil gravity scales - table of constants + CALTEX logo on back

DYNSTAT is a mechanical impact/resilience testing method popular in Germany (DIN 53435) for testing small samples of plastic ​

EDF = Electricitè de France - identical to model EDF 35 11 408 - table of values for single-phase lines in well of stock​ - table of maximum permissible intensity values on back

For calculating steel beams according size, weight, profile, etc based on formulae from Potzsch/Demulder/Gajac + two full-width open windows with cursor lines in back

Part of series for Czech stationer KOH-I-NOOR - copy of model 1694​

Simpler version of two Meteo models ​for weather forecasting - distance scales in both imperial & metric - black logo = early model

Early because lacking model no. + red outline of logo​ - longer than usual for pocket - two open windows with cursor line in back

Early because milky white original plastic + lacking model no. + red outline of logo​ - two closed windows with cursor line in back + table of constants om back

100% dummy - scale layout printed on sheet of plastic as shop window advertising item - also made half-size version​

Made for CONTROLEXACT (later version II for COMSIP AUTOMATION) - for calculating flow (liquid & gas) in valves & flowmeters - REVACO = registered trademark - unusual layout/design & striking cursor

Made for COMSIP AUTOMATION (original version for CONTROLEXACT) - for calculating flow (liquid & gas) in valves & flowmeters - REVACO = registered trademark - unusual layout/design & striking cursor

Designed for rapid & accurate calculating - circular but housed in square case - front & back shown as per instructions - slide also worked by metal wheel - table of gauge points in centre​

Uniquely slide is part of closed frame (no cursor) on back of stock​ - registered design commissioned by Shell Nederland Verkoopmaatschappij (SNV) for Heating Oil Inspectors to calculate efficiency levels (CO2, temperature & soot content) from exhaust gasses in the flue - read more ...

Uniquely slide is part of closed frame (no cursor) on back of stock​ - registered design commissioned by Shell Nederland Verkoopmaatschappij (SNV) for Heating Oil Inspectors to calculate efficiency levels (CO2, temperature & soot content) from exhaust gasses in the flue - read more ...

Shell-Mex & BP logo’s on back + one open window with 1 hairline in back + follow-on from earlier Central Heating Efficiency model made for Shell in NL (SNV)​ - read more ...

Top 3 scales are constants for Chromel, Iron & Chromel/Alumel - bottom 4 scales are for Chromel/Alumel (but smaller range) & Platinum/Rhodium (3 different %‘s) - scales on front of slide are for 2 different voltages of electrical couplings ​- inch scale on back