The dotted line from the earth to the moon represents your line of sight when looking at the moon. The large moon image shows what you would see at that point in the cycle. For the waning gibbous, third quarter, and waning crescent phases you have to mentally turn yourself upside down when imagining the line of sight.
Where can I find some general guideline for welding ventilation? For processes such as welding, brazing, soldering, and torch cutting, the primary purpose of ventilation is to remove air contaminants from the worker's breathing zone. Different ventilation strategies may be needed in each case to remove air contaminants from the welder's breathing zone. General guidelines have been published in CSA W117.2 Safety in Welding, Cutting, and Allied Processes, and ANSI Z49.1 Standard Safety in Welding and Cutting.
For stainless steels there are also gases available containing small amounts of hydrogen (H 2). The table indicates the appropriate choice of shielding gas for MIG/MAG welding, taking account of different types of stainless steel and arc types.or stainless steels there are also gases available containing small amounts of hydrogen (H 2). The table indicates the appropriate choice of shielding gas for MIG/MAG welding, taking account of different types of stainless steel and arc types.