Sum Coin Age(SCA) is the sum value of products of coin unspent transaction output alive days and its value. While the concept is similar to CDD, but SCA focuses on unspent transaction output. You can estimate the distribution of holders with these indicators.

$SCA=\sum_{u \in \text{unspent outputs}}\text{lifespan}_u*\text{value}_u$

SCA is an indicator that enables determining the sentiment amongst long-term-holders.

For every coin that has not been spent on that day, it accumulates one "Coin Day." To understand the concept of "Coin Day" better, check the examples below.

A UTXO for 1 BTC that has not been spent for 10-days has accumulated 10 coin days.

A UTXO for 0.5 BTC that has not been spent for 100-days has accumulated 50 coin days.

A UTXO for 8 BTC that has not been spent for 6-hours (1/4 day) has accumulated 2 coin days.

When that coin is unspent, the coin is considered "aged," and is being updated on the SCA metric.

SCA: An indicator shows the distribution of UTxO holders. It is calculated as the sum of the products of bitcoin unspent transaction output alive days and UTxO value.

SCDA: Similar indicator to SCA, but this indicator is calculated with USD value.