Here is an update of my drift measurement, almost 2000 h have past. Again, the reference wasn't pre-aged, only the z.t.c. temperature was measured, the oven adjusted to that temperature, the amplification adjusted to 10.000 00 V and the overall t.c. trimmed. The reference is sitting at the bench, supplied by a low noise lab power supply.
The reference is drifting downwards compared to F7000-1. By the eye the drift is not linear, but slightly curved, a sqr-fit matches best. Although, we are looking at 3.2 ppm of change, which is quite a lot. I'm tempted to stop it here and to perform a one week cooking, using the internal oven. On the other hand I could also build a second one. Not yet sure how to proceed.
Don't take the result too serious, this is only a single specimen and thus without any statistical significance.
-branadic-