Lens-Maker's Glasses

The Lens-Maker's Glasses is a item in Risk of Rain, giving you a 7%(might be 10%, though) chance to critically strike. When picked up, a red cross/plus sign will hang over your character's head.

When an attack critically strikes, it will make a sharp noise, and the damage text will be emboldened with a red outline.

Explanation about Stacking & Crit Chance
Each stack of linearly increases your critical chance by 7%. Normally, having at most 14 stacks of this item will guarantee you 100% critical chance.

However, a simple math calculation tells us: 7%*14 = 98%, not 100%. Here's why 14 stacks will give you 100% crit chance.

First, there's something about the Mechanism of Critical Chance in this game:
 * Every character starts with 1% crit chance at the beginning.
 * All crit chance increasing items, including (+5%), (+5%), (+6%) and (+7%), work on the crit chance together.
 * Although the value of crit chance is not capped (can go beyond 100%), being a "chance", crit chance is automatically capped at 100%.
 * Currently, we don't have any item/way to decrease the crit chance.

Second, there's a BUG on this item: This is a BUG because, unless your crit chance is 1%, picking up the first will only give you 7%. While decreasing crit chance through cheating, getting a 1st pair of glasses at 0% crit chance increases the chance by 7%, and getting a 2nd(/3rd/4th/...) at 1% crit chance still gives you +10%.
 * If crit chance is 1%, picking up a will raise crit chance by 10% (as what the in-game item description says), instead of 7%.

Considering the conditions above, on the following two kinds of situations:
 * If is the only crit-enhancing item that has been collected in the run, the crit chance on 14 stacks would be: 1% + 10%*1 + 7%*13 = 102% --> 100%.
 * If at least one of the other crit-enhancing items has been collected before the 1st pair of glasses, the minimum crit chance on 14 stacks would be: 1% + 5%(minimum value) + 7%*14 = 104% --> 100%.

Therefore, at most 14 pairs of glasses grant you critical strike on each attack.

Item Synergies

 * Harvester's Scythe - healing you each time you crit, as well as boosting your crit a small amount.
 * Predatory Instincts - giving you bonus attack speed each time you crit, as well as boosting your crit by a small amount.
 * Wicked Ring - reduces your cooldowns by one second each time you crit as well as boosting your crit chance.
 * Frost Relic - the icicles that spawn after you kill an enemy from Frost Relic can crit.
 * Brilliant Behemoth - the explosions can crit.

Trivia

 * The mailing location, Grievenkamp, is a reference to John E. Grievenkamp, an optical scientist.
 * Some said the stacking formula of crit chance was: (1 - (0.9)^x)*100, while x is the number of stacks. This multiplicative stacking formula DOES have a bunch of answers quite near to the real crit chance when variable x is not big enough. However, it's not difficult to see the problem of this formula when x > 10. Especially when x >= 14, the game provides critical attack on each attack, while the answer of formula is only around 77%. Tests are easy to do with Artifact Command.

es:Lens-Maker's Glasses