Copy your mortar's position off the map, then your target's, and paste them in below — exactly as the game shows them, like x67.60, y68.09. You'll get the distance in meters, which direction to face, and where to set the sight.
Math: range = 100 × √(Δx² + Δy²), azimuth = atan2(Δx, Δy), mil = deg × 6400 ⁄ 360.
Elevation is interpolated between the two nearest rows of the firing table, which was read off the sight in 50-mil steps.
The scale is even in mils but not in meters: one labelled interval covers 55 m around the 150 m mark but only 23 m up near the 684 m ceiling, so never read the range labels as if they were evenly spaced.
Since there are no ticks between the labels, the aim point is given as a percentage of the gap between the two nearest ones, and the sight picture puts the reticle at that exact position rather than rounding it to anything.
The envelope comes from where the tube actually stops, not from the printed scale: 900 mil elevating, which is the 110 M mark, and 100 mil depressing, which is 704 m. The sight prints --- in both columns past 150 mil, so the last row is shown that way in the picture even though its range is known — it was measured by firing at full depression, and a quadratic through the tail of the table had predicted 703.8 m for it.