1. To power meter, which type of adapter is more advantageous, universal adapter or interchangeable adapter? 
Actually no matter what type of adapter, its function is the same. To universal adapter, FC type is its default adapter, after screwing the FC type, it can be mounted on SC or ST. When FC connector is more popular in your network, it is a better choice. When you always use SC or ST connector in your network, it is recommended that you can choose interchange adapter SC, ST, which is fixed with SC or ST patchcords ( pigtails).

2. Can you provide certificate for calibration for any type of fiber test instruments? 
For power meter and light source, they are passed EMC testing, and Visual Fault Locator is certificated with CE.   For  OTDR, we have the certificate for calibration from China Defence & Fiber Optical Communication Station.

3. Can you develop 635nm VFL? What is max output power? 
We can do. Its max output power is about 0.8mW.

4. Is the portable carrying case included in the standard package? 
Yes, it is included, You should not pay the extra charges. For OPM, LS and VFL, it is with fabric bag. For Fusion    splicer, it is  with Al-alloy carrying case. For OTDR, it is with plastic carrying case with Al-alloy as frame.

5. While choosing OTDR, which parameter is more important?

Even if for a same main frame, this module is different on request of different dymanmic range. This popular

module is 37/35dB or 42/40dB.