Ivar_Rummelhoff

Here is my (edited) suggestion:

mouseMove
.Buffer(2, 1)
.Select(b => b[1] - b[0])
.Window(mouseDown, _ => mouseUp)
.Concat();

The Subtract method is not needed.

I had to change

var open = decimal.Parse(elements[1]);
var high = decimal.Parse(elements[2]);
var low = decimal.Parse(elements[3]);
var close = decimal.Parse(elements[4]);
var volume = long.Parse(elements[5]);

to

var open = decimal.Parse(elements[1], CultureInfo.InvariantCulture);
var high = decimal.Parse(elements[2], CultureInfo.InvariantCulture);
var low = decimal.Parse(elements[3], CultureInfo.InvariantCulture);
var close = decimal.Parse(elements[4], CultureInfo.InvariantCulture);
var volume = long.Parse(elements[5], CultureInfo.InvariantCulture);

in StockQuotes.cs.