The value of ⎕DCT determines the precision with which two numbers are judged to be equal when the value of ⎕FR is 1287. If ⎕FR is 645, the system uses ⎕CT.
⎕DCT may be assigned any value in the range from 0 to 2*¯32 (about 2.3283064365386962890625E¯10). A value of 0 ensures exact comparison. The value in a clear workspace is 1E¯28.
⎕CT and ⎕DCT are implicit arguments of the monadic primitive functions Ceiling (⌈), Floor (⌊) and Unique (∪), and of the dyadic functions Equal (=), Excluding (~), Find (⍷), Greater (>), Greater or Equal (≥), Greatest Common Divisor (∨), Index of (⍳), Intersection (∩), Less (<), Less or Equal (≤), Lowest Common Multiple (∧), Match (≡), Membership (∊), Not Match (≢), Not Equal (≠), Residue (|) and Union (∪), as well as ⎕FMT O-format.
For further information, see Comparison Tolerance .
⎕DCT←1E¯10 1.00000000001 1.0000001 = 1 1 0