How to Change the Window on a TI-84

The window is the rectangle of the coordinate plane that the calculator draws in. Every graph question you answer depends on it, and yet the settings are invisible until you press the WINDOW key and look at the numbers behind the picture.

Two problems bring students to this page. The first is a curve that has been drawn but cannot be read, because the interesting part is squeezed into a corner or the whole graph appears as a flat line. The second is a graph that refuses to draw at all, which usually means the window values are contradictory rather than that anything is broken.

This page explains what each value controls, when to reach for a preset instead of editing numbers, and how the window relates to the TABLE settings that so often get confused with it.

What each WINDOW value controls

Press WINDOW to open the screen.

A graph can only show you what falls inside this rectangle. A root that lies beyond Xmax does not exist as far as the drawing is concerned, even though the algebra says it does.

Editing the window by hand

Move between the lines with the arrow keys, type a value over the old one and press ENTER. Two details trip people up. The first is the sign: values below zero need the small negative key, not the subtraction key, and using the wrong one produces the kind of message our error code list describes. The second is consistency: Xmin must be smaller than Xmax, and Ymin smaller than Ymax, or the calculator reports a range error instead of drawing anything.

If a window is wider than about a hundred units, the tick marks and labels become unreadable and single pixels cover large spans of the curve. If it is narrower than a fraction of a unit, whole numbers disappear from the axes. Both extremes are signals that a preset would serve you better.

The Zoom menu presets

Press ZOOM for a list of presets that set the window in one keystroke.

• 6:ZStandard puts the view back to −10 to 10 on both axes, with a scale of one. It is the fastest way to find a curve that has wandered off screen.
• 4:ZDecimal sets X from −4.7 to 4.7 and Y from −3.1 to 3.1 on the TI-84 Plus, so one unit of X occupies exactly one screen step. On a colour-screen CE the limits are a little wider but the same pixel relationship holds. This is the preset to use when you want to read coordinates from the grid.
• 0:ZoomFit keeps your Xmin and Xmax and recalculates Ymin and Ymax so the curve fills the screen vertically. It is ideal when a curve has a large vertical range, and less useful when the shape of the graph is the point of the question.
• 5:ZSquare adjusts the window so that one unit is the same length horizontally and vertically. Circles come out round and right angles look like right angles, which matters for geometry and vectors.

Why a graph looks like a flat line

A line that appears horizontal is almost never a calculator fault. The vertical range of the window is simply too large for the slope you are trying to see.

Take Y1 = 0.01X, a very gentle line. In the standard window it looks perfectly flat.

Narrow the vertical range and the same function becomes an obvious rising line, which is exactly the habit to build: if a graph looks flat, the first question is what the vertical range of the window is doing.

The mirror-image problem is a curve that vanishes because it sits entirely above Ymax or below Ymin. 6:ZStandard first, then 0:ZoomFit, then a hand edit if neither gives the framing you want.

Why a smooth curve shows a corner

A parabola drawn in a very wide window can look as though it has a sharp point where the turning point should be. The calculator plots one point per screen pixel, joined by straight segments, so when a single pixel covers a large span of X the curve becomes a coarse polyline with visible bends.

The fix is to reduce how much of the plane is squeezed into each pixel. 4:ZDecimal does that by working in whole steps, and 2:Zoom In does it around the cursor when you need a closer look at one feature. If angles rather than coordinates matter, 5:ZSquare restores the equal axis lengths that a wide window had distorted.

How the WINDOW interacts with the TABLE

These two settings are separate, and that surprises people. The window decides what the graph screen shows; TblStart and ΔTbl on the TABLE SETUP screen decide where the table starts and how far apart its rows are. Changing the window does not move a single row of the table.

You can make them agree deliberately. Set TblStart to the same value as Xmin and ΔTbl to the same value as Xscl, and the table will list exactly the x-values marked by the ticks on your graph. That alignment makes it easy to compare a table row against the curve without converting anything in your head. The TABLE tutorial covers the setup screen in full.

If you are building a window around a question, it also helps to know where the curve crosses the axes. Our intercepts guide shows how 2:zero and 1:value return exact coordinates, which are a better basis for choosing limits than eyeballing the screen.

Before an exam

A window you can set in seconds saves real time, because hunting for a curve costs more than drawing one. Practise 6:ZStandard and 0:ZoomFit until they are automatic, and get into the habit of checking the axes labels before reading any value off a graph.

The SAT permits a graphing calculator on all of its maths questions, and the ACT permits one on the mathematics test only, with calculators that have a computer algebra system prohibited in both cases. Those conditions are summarised in our guide to whether TI-84 calculators are allowed, and the rules are revised from time to time, so confirm the current wording with the board before test day.