NVT Signal is a derivative of NVT Ratio by Dimitry Kalichkin which provides more emphasis on predictive signaling ahead of price peaks.
The calculation of NVT Signal is Network Value divided by the 90 day moving average of Daily Transaction Value. This differs from Standard NVT Ratio which is calculated by Network Value divided by Daily Transaction Value, the results are then smoothed with a moving average.
Data for Network Value and the USD value transmitted via Blockchain.info. Note the value transmitted on the blockchain is an estimation.