Help! help! How come Math pow( ) cannot work on this????

There is a mistake in gkaiseril's code that you copied. In general, it's a bad idea to try to copy&paste code snippets you find online without knowing what you are doing. You've admitted that you don't know anything about JavaScript, and you will have to work on that. Otherwise, it's impossible to create a Javascript solution to a problem. We all make mistakes, and sometimes these mistakes make it into sample code. You need to be able to look at a line of code and realize that it's wrong by knowing basic Javascript syntax. There is no way around that. Do yourself a favor and get a good introduction to JavaScript and read the chapters about the basic syntax. You will feel a lot more comfortable afterwards - and more competent - when it comes to figuring out what's wrong with a script.

For beginners, it's usually very hard to wrap your head around an expression that has a lot of layers (e.g. function call inside a parameter to another function call). It's easier to define your variables upfront, and then use them when you need them. Let me give you an example in pseudo code:

You are using something like this:

someVariable = someFunction(someConstant, someOtherFunction("a string").method);

Your code actually has a lot more parts to the expression. What you can do do make this a bit easier to swallow is break out the call to someOtherFunction() like this:

var functionArgument = someOtherFunction("a string").method;
someVariable = someFunction(someConstant, functionArgument);

As you can see, your line #2 is now much shorter, and easier to understand.

You can define your two variables that you need for the two form field values upfront, and then use them when you need them by just referencing the variables:

var mth = this.getField("mth").value;
var NY = this.getField("NY").value;

Once you get the basic formula working, you need to work on checking your input data and only calculate an output value is your input data is actually valid, but that's stuff for another day.

In order to access a field's value in JavaScript you can't just type the field's name. You have to use the appropriate methods and properties. So, for example, to get the value of a field called "mth" you need to use something like this:

var mth = this.getField("mth").value;

Then you can use the "mth" variable you've defined in the rest of your code.

I think I understood what the Math.pow part actually DID. I didn't understand what you wanted to do. You wrote

Math.pow(1-1.02,No. of years)

which gives the result I said. Because the first thing that must happen is 1-1.02 so what you write is EXACTLY the same as

Math.pow(-0.02,No. of years)

You probably want something more like

1-Math.pow(1.02,No. of years)

1. Converting from simplified field notation to full JavaScript is more than just choosing the option. Your JavaScript must do some of the things that were automatic in the simplified form. In particular, you must CONNECT every field you work with to a variable (except in some kinds of event, where you must NOT do this and have a special variable instead). Commonly, one uses getField to connect to variables. You must use "m" expecting it to contain the value of the field "m" - no, you can't, and that's why it is undefined.

2. Obviously something is very wrong with the formula as you've expressed it.  1-1.02 is always -0.02.

So for one year the result is pow(-0.02,1) = -0.02. For two years, pow(-0.02,2) = -0.02 * -0.02 = +0.004. For three years, pow(-0.02,3) = -0.02 * -0.02 * -0.02 = -0.0008. So your results are alternatively negative and positive, and rapidly get very small indeed. This is not a JavaScript issue, but a mathematical misunderstanding of something, to solve before coding.