diff --git a/2021/Day 1/rust_solution/src/main.rs b/2021/Day 1/rust_solution/src/main.rs
index 4222670..2806a66 100644
--- a/2021/Day 1/rust_solution/src/main.rs	
+++ b/2021/Day 1/rust_solution/src/main.rs	
@@ -12,6 +12,8 @@ fn first_puzzle(input: &String) {
 }
 
 fn second_puzzle(input: &String) {
+    // For each input, add it to a circular buffer whose write position is stored at the end.
+    // For all but the first two elements, output the sum of the circular buffer.
     let count = input.lines().scan([0; 4], |sliding_window: &mut [i32; 4], line|{
         let place = sliding_window[3];
         sliding_window[(place % 3) as usize] = line.parse::<i32>().unwrap();
@@ -22,7 +24,9 @@ fn second_puzzle(input: &String) {
         } else {
             Some(sliding_window[0..3].iter().sum::<i32>())
         }
+    // Filter out the first two elements, can't generate a three-element sum.
     }).filter(|sum| !sum.is_negative()).scan(0, |current, sum| {
+        // Subtract each successive elements, similarly to the first solution.
         let previous = *current;
         *current = sum;
         Some(*current - previous)}).filter(|diff| diff.is_positive()).count() - 1;