8Marking the original gauge length (L₀)

Each end of the original gauge length shall be marked by means of fine marks or scribed lines, but not by notches which could result in premature fracture.

For proportional test pieces, the calculated value of the original gauge length may be rounded off to the nearest multiple of 5 mm, provided that the difference between the calculated and marked gauge length is less than 10 % of $L_{\mathrm{o}}$. Annex F gives a nomogram for determining the original gauge length corresponding to the dimensions of test pieces of rectangular cross-section. The original gauge length shall be marked to an accuracy of $\pm 1 \%$.

If the parallel length ( $L_{\mathrm{c}}$ ) is much greater than the original gauge length, as, for instance, with unmachined test pieces, a series of overlapping gauge lengths may be drawn.

In some cases, it may be helpful to draw, on the surface of the test piece, a line parallel to the longitudinal axis, along which the gauge lengths are drawn.