The units used in the text are those internationally agreed on and called SI units or SIU, Systeme International d'Unit , or often as earlier also the MKSA system of units, depending on meter, kilogramme, second and ampere. The international abbreviation is SI (cf. references below). One distinguishes between two types of units, those of the first type being the fundamental units, of which the relevant ones for our purposes here are meter (m), kilogramme (kg), second (s), ampere (A) and kelvin (K), the last for thermodynamical temperature. All other units, like newton, hertz, etc. are derived SI units. The most important derived units for our purposes here, and possibly related uses, are summarised in Table 1, especially as a reference of internationally agreed symbols for the various units. ^[*] According to international agreement, symbols for units which are proper names, as in Table 1, are written with a first capital letter, their special names are written with small letters (e.g. hertz); plurals of unit names are formed according to the usual rules of grammar with irregular exceptions (hertz, siemens). Symbols for physical quantities are set in italic (sloping) type, while symbols for units are set in roman (upright) type. ^{[ ]} Multiplication of units is indicated by a raised dot (Table 1) or a space between the units (in text) (cf. again R.A. Nelson, above). Note that in the past ? ^?1 was occasionally described as mho with the MKSA unit of conductivity 1 mho...