Install blt by entering the following commands in the terminal:
sudo apt update sudo apt install blt
graphics extension library for Tcl/Tk - run-time
BLT is a library of useful extensions for the Tcl language and the popular Tk graphical toolkit. It adds a vector and tree data type, background execution and some debugging tools to Tcl, and provides several new widgets for Tk, including graphs, bar-charts, trees, tabs, splines and hyper-links, as well as a new geometry manager, drag & drop support, and more. . This package is a dummy package which depends on the current BLT library.