Single digit, Seven segment Numitron program and pcb design needed.

So the batteries would go inside the same compartment then as well.

Yes that is correct.

That has some serious consequences for the design, as the battery holder will be on the PCB. So the final design depends on the size/shape of the battery and it's holder.

Yes the battery shape is important, the watch itself i will be able to machine to any shape of pcb and battery as long as it is small.

I will probably use the same size battery in the original post link on hakaday. Looks like the battery was from sparkfun. 110mah 25 by 15 mm. The pcb can be bigger than the battery by a little though.

the only battery I see in that post is a 400 mAh Li-ion battery sitting next to the PCB.
If the battery is fixed, there's no real need for a supercap either. It doesn't add much time for your timekeeping if you run out of battery (and the RTC can do with as little as 1.3V or so, when your processor stopped working already - maybe even the boost converter). Can connect the battery backup pin directly to the main battery.

I saw the 110mah battery in the pdf in the charging cicuit.

In the parts list he shows both 110mah and 400. So i dont know what he is using.

I found this battery at Adafruit. Comfortable fit under the display.
A bit bigger capacity has this battery which would fit next to the display, broad side, making for an overall PCB size of 20x40 mm, and an overall thickness of about 15 mm.

The battery will cut off at 3V so a supercap would still come in useful to keep the time as the battery recharges.

This battery is from adafruit as well. It is more square but would sit under pcb as well.

Forgot the link.

That's the second one I linked to.

For the overall arrangement: the surface area needed for the components excluding supercap, battery, connectors and push buttons is a little more than the surface area of the display itself. Without battery, I had the supercap, buttons and display on one side of the PCB, the rest on the back - partly in between the pins of the display.
The various through-hole components (the display itself, the supercap) do severely limit how things can be arranged, though.

Ok sounds good, I know this watch will prob be bulky. The one thing I wanted to do. Was to keep the battery hidden from the front and have the PCB as sort of a watch face . i designed the watch to have a big open face. This way you can see the components. Going for kind of a steampunkish look. So the pcb needed to be either round or square and cover the battery. In other words i dont mind seeing all the components. I think if the pcb was even 1.5 inch round or square it would still be fine. I hope that made sense.

Ah, that way.
I was playing around with designs trying to minimise the total footprint by using both sides of the PCB, including space in between pins and so.
Most components, including the (SMD) push buttons, are very flat (1-2 mm high) compared to the display itself. So the display will be really sticking out that way.

I wznt to see some components scattered around the display, does not have to be all. Would be cool if there were like a group of resistors on one side the supercap on the other. I measures 1.5 inches on my wrist it is pretty big, 1.25 would be better.

This 350 mAh battery would be a very nice fit under a PCB of 0.87" wide (the same as the length of your display) and 1.65" long - so sticking out 0.6" on both sides of the display.

This one, 150 mAh, would allow for a smaller PCB. Still 0.87" wide, but shorter at just 1.25": 0.4" on either side of the display. Still enough space for the components.

I do assume you're thinking of traditional through-hole components for the resistors and capacitors, rather than the tiny 0603 size SMD ones?

But how about the supercap for time backup? Where to place that?

Also the buttons will prob have to be sideways, like on a normal watch so i might have to solder pins in at a 90 degree to the pcb and attach the buttons that way.

Yes small through hole components would work. Also you said a 50mF would give 40 bours of backup for rtc. Did you mean 50uf? I have some 47uf that are the same height as the numitron display.

Rough outline of PCB, 1.25x0.87".
ICs go on the bottom of this PCB. Too modern for steampunk look.
Battery also under the PCB.
No space found for the supercap RTC backup and boost converter... (supercap is indeed mF, so milli, not micro - in "can" package it can be as low and as narrow as the display and hold up to 470 mF, 5.5V).

The red patches next to the grey resonator are where two push buttons can go. One for time, one for date.

The display is just a placeholder for the image.

If you make the PCB 0.2" wider you could place the buttons against the short sides of the display (so you have something to push against). I'm sure there are push buttons that have the leads at a 90° angle coming out. That would also free up space on the left side of the PCB (where the resonator is) for a supercap. Still no idea on what to do with the boost converter.

The 350 mAh battery fits comfortably under this PCB.