The HUD, or "heads-up-display" is the small text display at the top of the screen which includes informations such as temperature, pressure, particle which your mouse is over, version, and speed (in Frames per Second or "FPS")

To toggle this display on and off, press the "h" key on your keyboard, This can be used to enlarge the field of gameplay and visibility.

The HUD is split into two parts, one on the right and one on the left. More information is displayed if you are in debug mode, which you can get into by pressing d. Also if you are using a beta, some of this extra info will always be displayed, even if you are not in debug mode and don't want it.

On the left, it displays Your current version. If you are using a beta, it will say that and also the build number of the beta. If you are in debug mode or using a beta, it will also tell you the number of particles on the screen, the number of generations life particles have been through, and the current gravity and air modes. Press w to change gravity modes. Mode 0 is vertical, 1 is radial, and 2 is no gravity. Press y to change air modes. Mode 0 is normal, 1 is no pressure, 2 is no velocity, 3 is no air, and 4 prevents air from updating at all.

On the right, it displays particle inforation. When you are not over a particle, it says Empty and the pressure at that square. If you are in debug mode, text below that will tell you your current mouse coordinates and the gravity at that spot. If you are over a particle, it tells you the name of the particle. Next, if you are in debug mode it will have the ctype in parenthesees if it has one. If particle you are over is lava and it has a ctype, it will display "Molten (name of ctype)". Next, it shows the temperature of the particle in degrees Celcius. The maximum temperature is 9725.85 degrees and the minimum in -273.15 degrees. If you are in debug mode or are using a beta, It will also display the life of the particle. If you are over a particle, the text below its information will not show the gravity at that spot, even though it exists. It will still display the mouse coordinates and also the index of the particle at that spot.

Here is an example of what the HUD would look like while over a particle in debug mode:

Left: Version 64.2 Beta (85) FPS: 61 Parts: 13549 Generation: 0 Gravity: 0 Air: 0

Right: SPRK (METL), Pressure: 0.43, Temp: 40.01 C, Life: 1

Right: #11519, X: 336 Y: 166