ERR:DATA TYPE means a command received the wrong kind of value — a list where a single number belongs, a number where a list name belongs, a matrix in a list operation, and so on. The math itself might be perfectly reasonable; the calculator just can't do it with the type of object you handed over. Here's how to spot the mismatch fast.
First move: use Goto
On the error screen, choose 2: Goto (not 1: Quit). The cursor jumps to the exact spot where the wrong type showed up. Then work through the command one argument at a time and ask: does this slot expect a number, a list, or a matrix — and what did I actually put there?
What "wrong type" looks like
The TI-84 keeps numbers, lists, matrices, and other objects in separate categories, and each command slot accepts only certain ones. Typical mismatches:
- A list where a number is expected. Feeding L1 into a command argument that wants a single value.
- A number where a list is expected. The stat plot case below is the classic example.
- A matrix in a list operation. List commands work on lists, not matrices — even if the matrix is just one row.
- Storing the wrong type into a variable. Trying to store a list into a plain number variable (or vice versa) with
STO→. - A complex or negative value where a positive real number is expected. Some commands demand a positive real input, and a negative or complex result from an earlier step trips them up.
The stat plot classic: Xlist set to a number
This one bites during stats homework constantly. Your stat plot's Xlist or Ylist is supposed to hold a list name like L1 — but somehow a plain number ended up there instead. When you graph, the plot tries to use that number as a data list and fails with ERR:DATA TYPE.
The fix:
- Press
2ndY=to open the STAT PLOT menu. - Select the plot that's turned on.
- Move the cursor to the Xlist: field.
- Press
2nd1to enter L1 (the L1 name lives above the1key). - Do the same for Ylist: with
2nd2for L2 if needed. - Press
GRAPHagain.
The key detail: L1 is a name you enter with 2nd 1 — typing the digit 1 by itself puts a number in the field, and that's exactly the type mismatch this error is about.
Solver and regression inputs
The equation solver and regression commands are the other frequent offenders. Each argument slot has an expected type, and it's easy to hand a regression a plain number where it wants a list name, or give the solver a list where it needs a single value. If 2: Goto drops you inside one of these commands, check the arguments left to right against what each one is supposed to be. Entering data for a regression and getting errors? The dimension-mismatch cousin of this problem is covered in /error-fixes/err-dim-mismatch/.
Diagnosis checklist
| Where the error hit | Likely mismatch | Fix |
|---|---|---|
Pressing GRAPH with a stat plot on | Xlist/Ylist holds a number, not a list name | 2nd Y=, set Xlist to L1 via 2nd 1 |
| A list command | You gave it a matrix or a plain number | Swap in an actual list (L1–L6) |
STO→ (storing a value) | Value type doesn't match the variable type | Store lists to list names, numbers to letters |
| Solver / regression | An argument is the wrong kind of object | Check each argument's expected type |
Still not sure which error you're even looking at? The full map of TI-84 error messages — what each one means and where its fix lives — is at /error-fixes/error-messages/.
Try the fix right now
You don't need your handheld to practice this. Open the free online TI-84 calculator — a full TI-84 Plus CE in your browser, no download required. Press 2nd Y=, open Plot1, and set Xlist to L1 with 2nd 1. Once you've entered a list name the right way one time, ERR:DATA TYPE loses its power to derail your homework.