Sch 2 para 36 Allowable stresses
(1) In paragraph 37, the following symbols have the following meanings— (a) R e/t , yield limit, indicates the value at the calculation temperature of— (i) the upper flow limit for a material presenting upper and lower flow limits, (ii) the 1.0 % proof strength of austenitic steel and non-alloyed aluminium, (iii) the 0.2 % proof strength in other cases. (b) R m/20 indicates the minimum value of the ultimate tensile strength at 20 o C. (c) R m/t designates the ultimate tensile strength at the calculation temperature.