Shades of color that are visible to the naked eye in a single-color print should appear the same to most observers.However, from a physical point of view there will always be differences, even when using a single batch of ink.
These differences should be imperceptible to the naked eye, but a well-calibrated spectro-densitometer can measure and express them mathematically. The important thing is that the differences, expressed as Delta E, remain below the standards.
For more information on this topic, refer to our document: Tolerancia de Color en Prensa.