<p>I have some decimal data that I am pushing into a SharePoint list where it is to be viewed.  I'd like to restrict the number of significant figures displayed in the result data based on my knowledge of the specific calculation.  Sometimes it'll be 3, so 12345 will become 12300 and 0.012345 will become 0.0123.  Occasionally it will be 4 or 5.  Is there any convenient way to handle this?</p>

As I remember it "significant figures" means the number of digits after the dot separator so 3 significant digits for 0.012345 would be 0.012 and not 0.0123, but that really doesnt matter for the solution. 
I also understand that you want to "nullify" the last digits to a certain degree if the number is > 1. You write that 12345 would become 12300 but im not sure whether you want 123456 to become 1230000 or 123400 ? My solution does the last. Instead of calculating the factor you could ofcourse make a small initialized array if you only have a couple of variations.
```
```
private static string FormatToSignificantFigures(decimal number, int amount)
{
    if (number > 1)
    {
        int factor = Factor(amount);
        return ((int)(number/factor)*factor).ToString();
    }

    NumberFormatInfo nfi = new CultureInfo("en-US", false).NumberFormat;
    nfi.NumberDecimalDigits = amount;

    return(number.ToString("F", nfi));
}

private static int Factor(int x)
{
    return DoCalcFactor(10, x-1);
}

private static int DoCalcFactor(int x, int y)
{
    if (y == 1) return x;
    return 10*DoCalcFactor(x, y - 1);
}
```
```
Kind regards
Carsten