Hi Florian,
nice watch you inherited from your granddad. Without seeing the inside and
having the movement and case number it is difficult to tell you details.
But let's do some speculation: IWC Electronic would say from the seventies,
most probably gold case 18ct or 14ct. Could be a Cal. 150. which is a tuning
fork movement patented by Bulova.
We don't discuss market values in this forum, but in general, mechanical
movements are more valued by collectors than electronic or quartz. However, if
the case is made of 18ct gold, there is a certain value to the case metal
alone these days.
Since it is a heirloom in your family and the watch is in good shape as we
could see from the images, keep it safe and pass it on to the next generation.
br
-Cromagnonman