Philips PDT-021/01 weird times

I collected a box of old darkroom accessories , in the lot a timer Philips PDT-021/01.
I don't care about paper calibration with the cell, and will use only the timing part.
The top right button is the power for the unit, and the left top button triggers the timer.

It seems obvious: push the green button (enlarger pictogram) down, set the time with the right wheel.
Units should obviously be seconds and for long exposure push down the red x10 multiplicator.
Not sure what the L/D is for. On the picture here unit is powered, a red needle is in the middle of the L/D arrows.

now, the weirdness is that I checked times with a chronograph and the figures by the right wheel are not seconds, but more like half seconds (not exactly).
I get repeatable measurements along all the scale (1 -> 15 and x10) but theses figures are not secs.

I'd open it up and determine how the timing is done. Probably a timer circuit that ultimately relies on an RC filter and the capacitor has drifted downward in value, perhaps? .

koraks said:

I'd open it up and determine how the timing is done. Probably a timer circuit that ultimately relies on an RC filter and the capacitor has drifted downward in value, perhaps? .

Click to expand...

before that I decided to change settings on the left wheel, just out of curiosity. And this modifies the time... So despite only the green button on, there's a shared circuitry. In fact the variation as per the inner markings of the left wheel means it adjusts as per paper grades, this can be induced by the markings. That's obviously dutch: Zacht Normaal Hard, left to right EH - H - N - S - Z - EH, not sure about the S...
Also there's like an adjustment screw on the left side of the body. So I will try to figure things out before opening....

antonio_b said:

not sure about the S...

Click to expand...

"Speciaal" most likely. A common term for the middle of the road grade 2 as we usually call it now.

I wonder if any source has the instruction manual that covers the way the timing works or can be altered such as Butkus?

pentaxuser