If is greater than unity, a bow shock will form ahead of the pitot tube as sketched in Figure 2.9. In ideal gases >1 if , the critical pressure ratio. The velocity at point 1 is then determined by relating it first to point 2 by the Rankine-Hugoniot conditions and then to 0 using reversible adiabatic equations given above. This is possible because the flow beyond the shock (at point 2 and 0) is subsonic. The pressure ratio in this case can be shown to be

Such calculations are best carried out using normal shock and isentropic gas tables.