Reticle size and zero

Goal of this article: set up the reticle’s coordinate space, and understand what the three parameters mean — because every element you add afterwards is positioned in terms of them.

The top section of the right-hand panel holds three things and a button:

Field	What it is
Name	What the reticle is called. It appears in the calculator’s reticle view when the file is loaded
Size (W×H)	The total angular field the definition covers
Zero (X,Y)	Where the aiming point sits inside that field, measured from the top-left corner
Set	Applies all three. Nothing takes effect until you press it

All four numbers are angular measurements, and you can type them in whichever angular unit you think in — mil, MOA, in/100 yd, cm/100 m. The unit you type is the unit stored in the file.

The coordinate space

This is the part worth getting straight once, because everything else depends on it.

Size is a rectangle of sky. A 12 × 12 mil reticle describes a 12 × 12 mil field; nothing outside it is drawn. It is not your scope’s field of view and it is not related to magnification — it is simply how much angular space your drawing needs.

Zero places the aiming point within that rectangle, measured from the top-left corner, X rightwards and Y downwards. For the shipped Mil-Dot reticle the size is 12 × 12 mrad and the zero is 6 / 6 mrad: dead centre.

Element coordinates are then measured from the zero point — and this is the flip that catches people:

• X is positive to the right, negative to the left.
• Y is positive upwards, negative downwards.

So a drop mark 2 mrad below the crosshair is at Y = −2, and the shipped Mil-Dot file draws its crosshair as a line from (−5, 0) to (5, 0) and another from (0, −5) to (0, 5), with a circle centred on (0, 0).

That is two different conventions in one dialog — the zero measured from a corner, the elements measured from the zero — and it is worth reading twice. The reason is that the zero is a property of the canvas, while elements are things you place relative to the crosshair.

Choosing a size

Since everything is scaled to fit the preview, the size does not change how big the reticle looks on screen. What it changes is proportion: a 20 mil-wide reticle drawn with 0.2 mil lines has finer-looking lines than a 6 mil-wide one drawn with the same 0.2 mil.

Two practical points:

• Make it big enough for the marks you need. If your BDC marks run 8 mil below the crosshair, a 12 mil tall reticle with a centred zero cannot hold them — you have 6 mil of room below.
• Off-centre zeros are normal for BDC work. Size 12 × 20 with the zero at 6 / 6 gives you 6 mil above the crosshair and 14 below, which is the shape a drop-compensating reticle actually wants.

At the other extreme, the shipped M16 iron-sight picture is 350 × 350 moa with the zero at 175 / 175 — an aperture sight subtends vastly more than a scope, and the numbers simply follow.

The status bar is your measuring tool

Move the mouse over the preview and the status bar reports the cursor’s position relative to the zero point, to three decimals, in the display unit chosen under View → Coordinate Display Units. Outside the drawn area it reads --.

That is the intended workflow, given there is no dragging: hover where you want something, read the coordinates off the status bar, and type them into the element dialog. It is also how you check a drawing — hover over a mark and confirm it is where you meant it to be.

Note that the display unit is a readout preference only. It does not convert the reticle, and it does not change what the element dialogs expect; those accept any unit you type.

Parameters first, elements second

The element type dropdown and all six operation buttons stay disabled until the reticle has a non-zero size. That is deliberate: an element position means nothing without a coordinate space to be positioned in.

So the order of work is always:

1. File → New (which starts you at 10 × 10 mil, zero at 5 / 5) or File → Open.
2. Set the name, size and zero, and press Set.
3. Add elements.

You can come back and change the size or the zero later — press Set again and the preview redraws — but be aware that element coordinates do not move with it. Changing the zero shifts where every element sits relative to the crosshair; changing the size can push elements outside the drawn field. Both are occasionally what you want, and both are easy to do by accident.

Next

Reticle elements — the six element types, the fields each one needs, and how draw order decides what covers what.

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