The upgrade chips I've found (so far) simply list stat boosts like "+1" to damage/reload/rate of fire/clip. I'm fairly sure these are relative boosts, not absolute, but beyond that I'm unsure of how they work. Stats aren't exposed directly, just via "meters" where the actual number of "ticks" seems to mean a different amount of damage/clip/etc per gun.

  • Do upgrades of the same type stack? Additive or multiplicative?
  • What percent or absolute value will each chip improve a stat by?
  • "Stats are exposed di" I think you accidentally a word or two. Feb 24, 2013 at 10:02
  • @galacticninja Fixed, I do that a lot when I stop one sentence to write another
    – Ben Brocka
    Feb 24, 2013 at 17:50

2 Answers 2


Upgrade circuits improve one of the 4 weapon stats (Damage, Reload, Clip, and Speed) by a relative flat amount depending on both the engine and tip used.

For example, +1 Speed on a shotgun barely increases the shotgun fire-rate, whereas +1 Speed on a sub-machinegun greatly increases fire-rate. However, regardless of the engine and tip, a +3 Speed circuit is always 3 times the improvement of a +1 Speed circuit.

You can see the increase that a circuit provides when installing it - the UI displays an extension on the bar indicating how much your stat will improve (green) or degrade (red). The increases from multiple circuits stack additively, but there is a cap on each of the 4 stats; when the bar for that stat in the weapon crafting screen is full then upgrading it further does nothing. Below you can see the bars in the weapon crafting UI: both tools have maxed Clip in this case:

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Also note that placing a chip in the upper or lower row improves the upper or lower tool, respectively. In some cases an upgrade circuit can affect both tools but I've personally only seen Reload affect both upper and lower tools with a single circuit.

When I hop on tonight I can update you with the exact scale factors per engine/tip and post screenshots so that this information is a little more clear.

  • Still working on collecting data, lots of combos! Anyone else who has values feel free to start a table and collect data that you have, this is a good com-wiki question.
    – Sadly Not
    Feb 22, 2013 at 2:05
  • Unfortunately I have almost no guns to test with, and I've been stingy with my crafting mats. I'm still on the first playthrough though
    – Ben Brocka
    Feb 24, 2013 at 17:54

The upgrade chips work relative to the type of weapon engine selected, and particular engines and tips are selective about what types of upgrades they'll best support. For instance, upgrading Damage on a Pulse Rifle (Military Engine + Repeater Tip) gives you a very poor return on investment, even with all chip sockets occupied, while upgrading Damage on a Contact Beam (Plasma Core + Precision Tip) increases the weapon's energy output greatly. Likewise, increasing clip size on the Pulse Rifle will give great increases in ammo capacity, up to twenty or so additional rounds, while upgrading the clip size on the Contact Beam gives negligible increases, at most garnering an additional couple of shots.

The values that are applied appear to be additive, instead of multiplicative. You'll receive the same increase in quality for each chip added from a particular category. As was indicated by the previous poster, certain values are applied to both tools at the same time, particularly the Reload stat. This is because when Isaac reloads the weapon, he reloads both tools simultaneously, so the weapon's reload time is determined by the slowest-reloading tool. By adding Reload chips to both tools, you can make a slow-loading gun, like the Rocket Launcher (Survey Charge + Directed Suspension Field) into a particularly fast one.

Ultimately, the number of "tick" increases that chips contribute to in the stat bars are arbitrary, based on the weapon, because of the bias each weapon has for its best upgrades. Upgrading clip size on a Rocket Launcher adds less than a quarter of a tick with each +2 circuit added to it, making it a very poor stat to upgrade.

Best thing to do is to experiment with engines that complement each other's reload times to get that out of the way, and then focus your chips on one particular skill that each gun excels at. Pulse Rifles are about fire rate, Contact Beams are about damage, etc. Only a few guns, like the Plasma Cutter, allow you to nearly max all their stat bars, so don't get too picky about it.

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