I have come across the recommended values for a Maintainability Index (MI) as follows:
Are these values are dependent on technology? For example, is a value of 70 good for Mainframes but difficult to maintain for Java?
Can use same yardstick independent of technologies?
It depends how the "Maintainability Index" is calculated. This doesn't seem to me like something which would work across languages simply because languages are so different.
It might seem reasonable to do a simple compare of "number of lines per function", but what happens when you try and compare C code which is full of pointers, or C++ code full of templates, or C# with LINQ queries, or Java with generics?
All of those things affect maintainability but can't be measured in any meaningful cross-language way, so how can you ever compare numbers between 2 languages?
I don't think you can put a number on how easy a piece of code will be for a developer to maintain.
Different people will look at the same code and interpret it in their own way, depending on experience, culture, reading comprehension, etc.
That being said, metrics would definitely be different across technologies. You're looking at completely different syntax, conventions, terminology, etc. How can you quantify the difficulty difference between low level mainframe code and a high level language like Java or C#?
I think metrics are good for one thing, and one thing only: guidelines. In terms of code quality, I don't think they should be used for anything other than describing a code base. They should not be used as a determining factor of difficulty or "grok-ability".
This is an explanation about meaning of maintainability index value.