# What is the algorithm used to calculate the 3-point OSNR in the WaveAnalyzer?

To determine the OSNR you need to calculate the powers at the 3-point OSNR locations (Psignal, Pleft, Pright).

1)      Take a scan using the lineardata command with 150 MHz resolution. It’s important to retrieve the data in units of mW rather than dBm using this command:

http://<ip>/wanl/lineardata/text

2)      Select two noise windows of 12.5 GHz width on either side of the signal. Integrate to find the total power within each to give you Pleft and Pright.

3)      Select a 12.5 GHz window centered on the signal. Integrate to find Psignal, the signal power.

4)      Calculate the OSNR ratio using the following formula.

5)      Convert the ratio to dB using the following equation:

An explanation on how to integrate the power within a specific frequency window is given in this article:

How to do I integrate power over a specific frequency window?