Why does TensorFlow start learning from the 1800th step?

01

It could be because of this:

Typically with quantization, a model will train with full precision for a certain number of steps before switching to quantized training.
The delay number above tells ML Engine to begin quantizing our weights and activations after 1800 training steps.

medium.com/tensorflow/training-and-serving-a-realtime-mobile-object-detector-in-30-minutes-with-cloud-tpus-b78971cf1193

But I have never set it to 1800 explicitly, and default it 500000: