Unlike the modern symbols, these ones consisted of straight lines only rather than filled in blocks which would have been less practical on a hand drawing. A reduced set of these symbols were used on teleprinters used for distributing weather information and warnings.
These symbols differed from modern equivalents in that they were composed solely of straight lines, unlike the filled-in blocks which might not be as convenient for manual drawing. A smaller selection of these symbols was employed on teleprinters to transmit weather data and alerts.