Wavelength can be tuned by turning the knob (potentiometer).

We have tested it with SLD broadband source and 0.1nm-RBW OSA. Actual tuning wavelength range: 1517.66 - 1563.86nm (tested value). Extinction ratio looks good, see optical spectrum at 8th photo.

See our test data below:
Set wavelength at LCD display (nm);  Tested wavelength at our lab (nm), 3dB-bandwidth(nm), Insertion loss(dB)
(including one connector loss):
1533.8, 1517.66, 1.83, 5.53
1560.1, 1550.005, 1.15, 4.03
1576.0, 1563.86, 1.13, 2.97

Last photo is from different sample of same model (Our store Product Code: OTI-TF-002),  this photo will help you understand following tips:
You can recalibrate LCD display wavelength by adjusting the 3 screws behind the LCD driver module, (adjusting by screw drivers, after open the enclosure top cover.). One screw is for LCD display range. 2nd screw is for wavelength coarse tuning of LCD, 3rd screw is for wavelength fine tuning LCD. The wavelength in LCD display will drift very slowly, especially after long time, but actual wavelength is very stable.  

The instrument is quite heavy, about 13kg net weight.

General Features
•Manual Wavelength Tuning
•Wavelength Range: 1514.5-1562.8 nm
•External Wavelength Input Connection
•Wavelength Monitor Connection
•Optical Input and Output Connections
•Status LEDs