Originally Posted by Trakhak

The digital readout might not have shown pressure because after a year, there would have been very low pressure in the tires.

The wheels of an early '70's Schwinn Continental usually can't be relied on to retain tires reliably at pressures much above 70 psi, even if the tire labels indicate that they can take a higher maximum pressure.

Riding at 30 psi might feel OK but runs the risk of damaging the tires or rims or both from hitting a pothole.

You should keep the pressure at around 65 or 70 psi.