For physical mounting and first-time login, the Huawei ATN910C Installation Guide covers step-by-step physical installation and basic ATP (Assistant Tool Platform) configuration.
The "best" manual is actually from Huawei’s support portal: huawei atn 910cg manual best
"Manual" is a broad term. To get the best information, you need to select the specific document type that fits your goal: For physical mounting and first-time login, the Huawei