如何重設計數器

目的：原始值是 origVal，我們想要透過增加/減少來更新到指定的數字

怎麼做？

1. origValue = origValue + expectedValue
2. diff = expectedValue - origValue
3. origValue = origValue + diff

範例：origValue = 54，newValue = 50

1. origValue = origValue (54) + expectedValue (50) = 104
2. diff = expectedValue (50) - origValue (104) = -54
3. origValue = origValue (104) + diff (-54) = 50