The verb centigrade uses names t1, t2, and t3 in its definition, but if you refer to them outside the verb they are not defined.
centigrade 32 0 t1 ¦value error t1 =. 123 t1 123 centigrade 212 100 t1 123
The use of t1 inside the definition of centigrade has not conflicted with your use of t1 outside the definition. The verb centigrade does not define a t1 outside of itself, as indicated by the value error, and setting a value into its t1 does not change the value of t1 outside the definition.
The t1 used inside centigrade is a local name. A local name exists only inside the verb. The t1 used outside centigrade is a global name. A name defined in the execution of a verb with the copula =. is a local name.