The deviation from the straight line of a tube length in mm per meter applies as measure of straightness for tubes. Tubes should be aligned straight according to the eye; complete straightness cannot be guaranteed. Special requirements have to be agreed, if applicable. For precision steel tubes with a diameter over 15 mm, according to DIN 2391, 2393 and 2394, 0.25 % of the gage length and for grades with yield stresses over 500 N/mm², 0.30 % of the gage length are valid. Requirements to straightness are determined in the dimension standards or are agreed especially. Mostly they can be fulfilled by special straightening only.