Perhaps the meter adjustment pot in the Astron is noisy or loose.
I have around 5 Astron PS. On each and every one I have to periodically clean and re-adjust the metering pots. The meters do not read directly. I have precision 1 ohm and 0.5 ohm 250 watt resistors that I use to check PS current draw. That makes it easy to know how much exactly current a PS is delivering without setting up an accurate current reading circuit. A good DVM will tell you the exact output voltage.
Clean and adjust the two metering pots so the meters read correctly.