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README.md

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+Suppose that _T_ is the correct time (remote time) and our local time
+is offset by _θ_.
+
+To determine _θ_, we perform these steps:
+
+1. \(A) sends a request to (B) at _t₀_ (local clock)
+2. \(B) receives and answers (A)'s request at _t₁_ (remote clock)
+3. \(A) receives (B)'s answer at _t₂_ (local clock)
+
+These steps are represented in the following diagram:
+
+```
+            t₁
+(B) --------^--------> T
+           / \
+          /   \
+(A) -----^-----v-----> T + θ
+         t₀    t₂
+```
+
+Bringing _t₁_ to the local time (between _t₀_ and _t₂_):
+
+t₀ < t₁ + θ < t₂
+
+So,
+
+* θ > t₀ - t₁
+* θ < t₂ - t₁
+
+But since _t₁ ∈ [⌊t₁⌋, ⌊t₁⌋ + 1)_, then:
+
+* θ > t₀ - ⌊t₁⌋ - 1
+* θ < t₂ - ⌊t₁⌋
+
+**Note**: Observe that the closer _t₁_ is to _⌊t₁⌋_ or _⌊t₁⌋ + 1_,
+smaller is the error in one of the two equations above.
+
+We can repeat the above procedure to decrease the range of possible
+values for _θ_. The ideal delay _d_ before sending the next request is
+calculated so that the next value of _t₁_ is close to a "full" second:
+
+t₂ + d + (t₂ - t₀)/2 - θ = ⌊t₁⌋ + k, k ∈ ℤ
+
+⇒ d = ⌊t₁⌋ + k + θ - t₂ - (t₂ - t₀)/2 mod 1
+
+⇒ d = θ - t₂ - (t₂ - t₀)/2 mod 1