ARCHIMEDES II is an orbital laser. Effective only outdoors in a limited radius and requiring a long recharge.”— Veronica Santangelo
The raw power of the sun, contained in an easy-to-carry package! Just point the handheld rangefinder at the bad guys, and pull the trigger!”
The C-Finder is not a weapon per-se: it is actually a handheld rangefinder linked to an orbiting laser weapon, the Archimedes II. When used, it communicates with the platform, identifying the "C" (position of the target) and calling down the orbital strike. Due to a slight delay between marking the target and the actual strike, the target can be changed before the laser beam hits the designated area.
In order to use the weapon at all, the Archimedes II has to be powered up by directing power to it at Helios One. Once the energy is directed to a destination, the action cannot be reversed. Even when the weapon is active, the orbital laser can only be used once every 24 hours.
For obvious reasons, the rangefinder does not work indoors. It doesn't deal any direct damage either (all of the destruction comes from the laser beam).
In Freeside, outside of Mick & Ralph's, the player character can find Max during the day. Max thinks the weapon is actually just a toy, as it is reminiscent of the popular 1950s-60s toy laser guns for children. The player character can pay Max 1000 bottle caps, or 20 bottle caps with a barter skill of 45 or more, for his "toy gun" Euclid's C-Finder.
Otherwise the player character can wait until Max goes to bed, usually after 9pm, then pickpocket the weapon from him, followed by a loss of karma. The game has been known to say "talk" rather than "pickpocket" Max when doing this. The interact button activates the pickpocketing menu, where the rangefinder can be stolen at no karma loss.
You can buy multiples of the rangefinder by returning to Freeside after some time. If Max is chasing the girl again talk to him and he will have a new rangefinder.
- Euclid's C-Finder cannot be used in V.A.T.S.
- If you have Veronica as a companion, she will respond to the weapon when first fired saying "Yeah, I guess it works."
- Though a heavy weapon of 15 lbs, Max, the child who owns it, has no problem holding it in one hand.
- If you fire the weapon during its recharge time, the positioning lasers will be seen but the weapon will not fire, however the weapon will fire immediately after the recharge time is over.
- The weapon will not always fire if the recharge time of 24 hours is waited using the wait-function instead of passing it in the game without the wait-function.
- Because the game does not allow the player to kill children, they will be knocked out when hit by this weapon.
- Euclid's C-Finder's reloading animation is exactly the same as the alien blaster's (when multiple charges are possessed), save for the C-Finder having an orange power cell, as opposed to the alien blaster's blue.
- Euclid's C-Finder does not work indoors.
- The sun ray causes a knock down effect in a large AoE where it is blasted so be careful with friendly fire, as your companions can be easily crippled by it.
- After finishing That Lucky Old Sun, in third person, the C-Finder's display will fully display the 'notifications' that the C has been found, and the notification that the laser will strike down, but there's no laser that will strike down.
 Behind the scenes
- Euclid was a famous Greek mathematician, known as the originator of many basic geometric and mathematical principles. Euclidean geometry and Euclid's algorithm for calculating the greatest common factor of two integers are both named for him.
- The name Euclid's C-Finder, and the graphics it shows the player while it is operating, are a reference to using Euclidean geometry to find the third point, C, of a triangle, given points A and B, and distances BC and AC. In this example B is the player's position on the ground, A is the position of the Archimedes II satellite, and C is the position of the target. The satellite gets distance BC from Euclid's C-Finder (which is described as a "handheld rangefinder", in the terminal notes at HELIOS One), and knows AC, one assumes, from radar height measurement. In practice, the satellite would also need to be able to determine the direction Euclid's C-Finder is pointing. Presumably, Euclid's C-Finder can only measure basic compass heading and range, leaving the satellite to calculate the target's elevation, unless it had an internal gyroscope and GPS, which would allow the elevation of the target to be calculated.
- inventory. It is possible Euclid's C-Finder may re-spawn multiple times on Max. If you do not have the gun in your inventory and return to Freeside some time after acquiring it, Max will have another Euclid's C-Finder . This will also result in additional ARCHII Charges added each day for each Euclid's C-Finder in the player characters
- Heave Ho! perk, firing Euclid's C-Finder may freeze the game. To fix this a player user can remove the perk using console commands, this will allow the player to fire the weapon without crashing. If the player character has the
- When trying to fire, the targeting laser may repeatedly play its animation without the laser firing. To fix, save the game with the gun drawn and firing and then quit the game completely back to the desktop/reset console. Restart, reload, and wait for the firing animation to complete. Ensuring to save far enough away from the target to not be hit, but close enough that the animation is still visible and playing.
- Sometimes the gun will not get any ammunition after activating Archimedes II, or it will fire a few times and then not get any more ammunition. To fix, save the game and the quit to the desktop/reset console. Reload the saved game and then after some time the charges will spawn as normal.
- Sometimes Euclid's C-Finder will not fire at all, only the lasers will be seen. However, the gun will also go off at a random time after this.
- I Could Make You Care, could bug the quest. See the page quest page for details. Obtaining Euclid's C-Finder before completing or at least initiating the quest
- unarmed" kills as evidenced by getting the Beautiful Beatdown perk while using it. The game seems to register kills with Euclid's C-Finder as "
- Silver Rush in Freeside, even after killing them. Euclid's C-Finder may disappear from the player characters inventory after being caught stealing from the
- The Thorn or fast traveling with Euclid's C-Finder in your inventory, it may fire a beam with no warning, hitting The Courier, their companions and any other non-player character's in range. After Exiting
- Archimedes II the C-finder will have two charges, the first will fire normally, however the second will charge but will not fire. You will see the targeting laser animation - three lasers that circle the target and meet in the middle - but there will be no damage and as added downside the animation will loop indefinitely every 5–10 seconds following your crosshairs no matter what weapon you have equipped. The only known fix is to save the game, reload the the save, but this will however not fix the C-finder from firing blanks, just the targeting laser loop. Sometimes after activating
- If aimed at a lake or body of water, there will be a bright flash of light, but no laser.
- If you obtain a second Euclid's C-Finder, repairing them may cause the bug in which it does not fire, and will show the laser marks only repeatedly even with another weapon out and may not fire.