Netum NT-W6 Quick Setup Manual page 15

For Example Custom @
as prefix
Step 1: scan "custom prefix"
Custom Prefix
Step 2: To set these values, scan a four-digit number (i.e. four bar codes) that corresponds to ASCII values.
See Numeric Bar Codes in appendix 1. Scan 1043(@) one by one.
Step 4: Set Data Transmission Format
<PREFIX> <DATA >