Why And how to use static readonly modifier in C#

Well I was been studying about Destructor, which influenced me to constructors once again ... So started some googling and testing than I faced something like this ..

public class Teacher
{
    private static DateTime _staticDateTime;
    private readonly DateTime _readOnlyDateTime;
    /*Resharper telling me to name it StaticReadolyDateTime insted of _staticReadolyDateTime*/
    private static readonly DateTime StaticReadolyDateTime;

    static Teacher()
    {
        _staticDateTime = DateTime.Now;
        /*ERROR : Thats oke as _readOnlyDateTime is not static*/
        //_readOnlyDateTime = DateTime.Now;
        StaticReadolyDateTime = DateTime.Now;
    }

    public Teacher()
    {
        _staticDateTime = DateTime.Now;
        _readOnlyDateTime = DateTime.Now;
        /*Error : Why there is an error ?*/
        StaticReadolyDateTime = DateTime.Now;
    }
}

I made three private attributes of static, readonly, static readonly

As they are private attributes I named them with _prefix. But my resharper telling me to rename _staticReadolyDateTime into StaticReadolyDateTime (ie as it is static readonly, may be). Is it oke with the naming convensions ?

on the other hand I am unable to use the static readonly attribute in public constructor, but using that static and readonly one easily.(ie even using it in static constructor)

than i googled to find out more, most of them are saying static readonly should only used in static constructor but not saying why ?

so I need to know some usages of static readonly modifier and its best uses and limitations. Difference with const, static, readonly will be even better ... :)

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A non-static readonly member can only be set in the class or a non-static constructor.

A static readonly member can only be set in the class or a static constructor.

Hence, it is illegal to set a static readonly member in your non-static constructor. Note that there is nothing wrong with reading the static readonly member anywhere you want in the class; the restriction is just on where you can write it. If you don't want the restriction, don't call it readonly .

---

readonly can be set only in constructor. Once set, it acts like a constant which cannot be modified. And for static readonly it needs to be set in static constructor.

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