A true "by IMEI fixed" calculator means you enter only the IMEI (no need for a login or server ping) and it outputs a code instantly.
This is the standard method for V4 devices. Specialized unlocking boxes (hardware used by repair shops) and paid server services utilize databases of encrypted hashes (often referred to as "hashes files" or "OemInfo"). The tool matches the device's specific hash against the database to find the correct unlock code. This is a paid service because access to these databases requires licensing fees. huawei v4 and v5 unlock code calculator by imei fixed