Offering a good quality wheter is is DIY or professional use a single compound gauge with manifold. It is mainly for refrigeration and air conditioning systems. Compound gauge means that you can display and measure both positive pressure and vacuum (inHg).
Vacuum scaling is displayed max 30 inHg. 30inHg is -1 bar negative pressure. 

This AC single gauge manifold has inner rings set up for R22, R134a, R404a and R410a refrigerants. These are the most common refrigerants nowadays that an HVAC technician will use. The proper way to use this AC charging gauge manifold is if you use PTC (pressure-temperature chart) with it. It is attached below.
You can also see the read that eg. 100psi corresponds to 32 degrees of R410a. Our single charging gauge is scaled up to 800psi and 55bar.
The manifold and its valve have made of durable aluminium material and have a sigh glass where you can follow the charging process and flowing the refrigerant. 

Both ports are 1/4" SAE male.