private void button2_Click(object sender, EventArgs e)
        {
            decimal[] tensionemisurata = new decimal[48];
            decimal[] correntemisurata = new decimal[48];
            int[] ore_i = new int[48];
            int[] minuti_i = new int[48];
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Filter = "measures file|*.txt";
            openFileDialog1.Title = "selezione un file contenente le misure";
            if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                string file = openFileDialog1.FileName;
                var sr = File.ReadAllLines(file);
                for (int i = 0; i < sr.Length; i++)
                {
                    if (i < 48)
                    {
                        var valPerLine = sr[i].Split('$');
                        tensionemisurata[i] = Convert.ToDecimal(valPerLine[0]);
                        correntemisurata[i] = Convert.ToDecimal(valPerLine[1]);
                        ore_i[i] = Convert.ToInt16(valPerLine[2]);
                        minuti_i[i] = Convert.ToInt16(valPerLine[3]);
                    }
                    else
                        break;
                }
            }
        }