Getting incorrect output in C# when dividing two decimals

Question

I have a program which divides a variable with another variable. But the answer im getting is incorrect:!! Please check image below :

Code Below:

      iter_defects++;
      df1[iter_defects].blob_id = b.Id;
      decimal convertX = Convert.ToDecimal(txtmmtopixX.Text);
      decimal convertY = Convert.ToDecimal(txtmmtopixY.Text);
      df1[iter_defects].count = iter_defects;

      df1[iter_defects].cog_X = Math.Round( Convert.ToDecimal( b.Centroid.X)) / convertX;
      df1[iter_defects].cog_Y = Math.Round(Convert.ToDecimal(b.Centroid.Y ))/ convertY;
     if (df1[iter_defects].cog_X > 10 && df1[iter_defects].cog_X < 30)
      {

     if (df1[iter_defects].BY > 1 && df1[iter_defects].BY < 74)
      {
       df1[iter_defects].cog_X = df1[iter_defects].cog_X - 20;

       }

      if (df1[iter_defects].BY > 64 && df1[iter_defects].BY < 129)
        {
         df1[iter_defects].cog_X = df1[iter_defects].cog_X - 20;

         }

      if (df1[iter_defects].BY > 118 && df1[iter_defects].BY < 183)
         {
           df1[iter_defects].cog_X = df1[iter_defects].cog_X - 20;

         }

       }

b.centroid.X and b.centroid.Y are double by default, so im converting it to decimal.

If I divide 147 by 9.3 i should get approx 16, but im getting 7.9!

Earlier I was using double instead of decimal, but even decimal is giving same issues. Have pinned the variable values on the image on the right.

What could be wrong?

UPDATE:

In my nested if statement I so some more arithmetic operation based on few conditions. When I removed those conditions the calculation is happening just fine. More confused now. The code below works, but without those conditions, my code after this section wont work:

  iter_defects++;
  df1[iter_defects].blob_id = b.Id;
  decimal convertX = Convert.ToDecimal(txtmmtopixX.Text);
  decimal convertY = Convert.ToDecimal(txtmmtopixY.Text);
  df1[iter_defects].count = iter_defects;

  df1[iter_defects].cog_X = Math.Round( Convert.ToDecimal( b.Centroid.X)) / convertX;
  df1[iter_defects].cog_Y = Math.Round(Convert.ToDecimal(b.Centroid.Y ))/ convertY;
 if (df1[iter_defects].cog_X > 10 && df1[iter_defects].cog_X < 30)
  {
  df1[iter_defects].cog_X = df1[iter_defects].cog_X - 20;
  }

Answer 1

It's not entirely clear how your program works, but I assume the problem is probably because you are in a loop of some kind and by the time you are checking your results, more than one iteration has occurred and the base values (ex cog_X ) have changed, so your comparison math won't match.