Preferred number
（重定向自Modular coordination）
![This graph shows how any value between 1 and 10 is within ±10% of an E12 series value, and its difference from the ideal value in a geometric sequence](/Images/godic/202501/27/E12_series_tolerance.svg0223.png")
![Two decades of E12 values, which would give resistor values of 1 Ω to 82 Ω](/Images/godic/202501/27/E12_values_graph.svg0223.png")
![A decade of the E12 values shown with their electronic color codes on resistors.](/Images/godic/202501/27/Preferred_values_05_Pengo.svg0223.png")
In industrial design, preferred numbers (also called preferred values, preferred series or convenient numbers) are standard guidelines for choosing exact product dimensions within a given set of constraints. Product developers must choose numerous lengths, distances, diameters, volumes, and other characteristic quantities. While all of these choices are constrained by considerations of functionality, usability, compatibility, safety or cost, there usually remains considerable leeway in the exact choice for many dimensions.