To find the coordinates of the points of interest: drop a vertical line from the Point to the X axis, and extend a horizontal line from the Point to the Y axis. Here are the lines associated with the two colors to be mixed. I have Magnified a portion of the "Y" axis to show how I have counted the number of pixels between the Y units given. The value of the Y ordinate will be:

Y = YScale + (NPixels ÷ 370). Note both the X and Y scales increment in values of 0.1, which is why I divided the number of pixels by 370 instead of the actual 37 pixels there are between values.

For example: The Horizontal line from the White Point to the Y axis intersects the Y axis at:

Y = 0.3 + (7 ÷ 370) = 0.3189 = 0.319

I have not shown the "X" axis as it works the same way with the formula:

X = XScale + (NPixels ÷ 370) = 0.3 +(4 ÷ 370) = 0.3108 = 0.311

The X-Y coordinates for the White Point are (0.311, 0.319). These are accurate enough to determine distances between points of interest.