Converting problem in a methode.

Dear Experts,

I programm in VS2010 and I use C#. I have this code but it has an error.
I have marked the codeline with an arrow that has the error :

        private void btnSwUnit_Click(object sender, EventArgs e)
        {
            Properties.Settings.Default.IsMGDL = !Properties.Settings.Default.IsMGDL;
            Properties.Settings.Default.Save();
            if (Properties.Settings.Default.IsMGDL)
            {
                btnSwUnit.Text = "Switch to mmol/l";
                lblSwUnit.Text = "Glucose Units: mg/dl";

                int eValInt = Convert.ToInt32(spdMinVal.Value) / 18;
                spdMinVal.Value = eValInt;
            }
            else
            {
                btnSwUnit.Text = "Switch to mg/dl";
                lblSwUnit.Text = "Glucose Units: mmol/l";

                double eValue = Convert.ToDouble(spdMinVal.Value) * 18; 
                spdMinVal.Value = eValue; <==========

            }
        }

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Error:
"Cannot implicitly convert type 'double' to 'decimal'. An explicit conversion exists (are you missing a cast?)".

How can I solve this?

Greetings,

Peter Kiers