> ## Documentation Index
> Fetch the complete documentation index at: https://stem-docs.intellectualpoint.com/llms.txt
> Use this file to discover all available pages before exploring further.
# SD card and bed leveling
> Insert the SD card, then level the bed with the paper test - the single most important skill for good prints.
## The most important skill in 3D printing
If your first layer sticks evenly, prints succeed. If it does not, they fail. **Bed leveling** sets the nozzle the perfect distance from the bed - about the thickness of a sheet of paper - across all four corners. This page takes your time and patience, but it is the skill that makes everything else work.
You will need a sheet of **printer paper** and the **SD card** (in the white flash-drive reader from the parts bag). Get the bed-leveling G-code files onto the card first (see the note below).
## Download the leveling files
Copy these three files onto your microSD card before you start. Use **M1** if you have an 8-bit board (older Ender 3) or **M2** if you have a 32-bit board (Ender 3 V2 / newer) - if unsure, try M2 first.
Leveling routine for **8-bit** Ender 3 boards (M0 pause).
Leveling routine for **32-bit** Ender 3 boards (M25 pause).
The squares test print you run after leveling.
## Insert the SD card
Pull the microSD card from the flash-drive reader. Use the reader's USB end to copy the bed-leveling G-code files (`STEM_M1`, `STEM_M2`, and `STEM_bed_level_print`) onto the card from your computer. Do not lose this tiny card.
Push the microSD card into the slot on the front of the printer, **contacts facing down**, until it clicks.
## How the leveling knobs work
Under each corner of the bed is a large knob on a screw. This is the key relationship:
Loosening a knob raises that corner of the bed **up** toward the nozzle.
Tightening a knob pulls that corner of the bed **down** away from the nozzle.
## Start from a raised bed
At each corner, spin the knob so the bed rises as high as it goes (the screw nearly disappears). Keep a finger under the screw so the knob does not fall off. Do all four corners.
## Run the leveling routine
On the LCD, click the knob to open the menu. Go to **Print from TF card → STEM\_M2 bed level → Print**. The printer homes itself using the limit switches, then pauses.
Select **Resume**. The nozzle moves to the **front-left** corner.
Slide a sheet of paper between the nozzle and bed. Tighten that corner's knob (which lowers the bed) until the paper slides with a **light scratch** - a "4 out of 10" of resistance. Not free (too far), not ripping (too close).
Click the knob to advance the nozzle to each corner in turn - front-left, back-left, back-right, front-right - and repeat the paper test at each. Aim for the **same feel** at every corner.
The routine sends you to the center to check, then back around all four corners. Leveling one corner slightly un-levels others, so a **second full pass** fine-tunes everything.
## The paper-test feel
| Feel | Meaning | Fix |
| ------------------------------ | ---------------- | ---------------------------- |
| Paper slides freely | Nozzle too far | Loosen the knob (raise bed) |
| Paper rips or won't move | Nozzle too close | Tighten the knob (lower bed) |
| Light, even scratch (\~4-6/10) | Just right | Move on |
Consistency matters more than perfection. The goal is the **exact same light scratch at every corner**. The second pass is where it comes together - do not skip it.
The SD card is seated, you have completed two full passes of the paper test, and all four corners plus the center have the same light-scratch feel. You are ready for a test print.
## Up next
Time to prove it works - run the **print bed test** and read the results.