System Variable FPC

⎕FPC - Floating Point Control

Z←⎕FPC returns the current value of the Floating Point Control precision.

Z is an integer scalar that represents the current value of the number of bits of precision used for VFP numbers.

⎕FPC←R	sets the value of the Floating Point Control precision to R.
⎕FPC←⍬	sets the value of the Floating Point Control precision to its system default state.

The minimum value for ⎕FPC is 53; the maximum value is the largest positive 32-bit integer 2147483647.

The system default value is 128.

For example, (note: these numbers are normally one long string of digits; they are broken here, with the break shown by {continued) for your convenience in reading)

      ⎕PP←200
      ⎕FPC←64  ⋄ *1x
2.71828182845904523543
      ⎕FPC←128 ⋄ *1x
2.718281828459045235360287471352662497759
      ⎕FPC←256 ⋄ *1x
2.71828182845904523536028747135266249775724709369995957 (Continued)
4966967627724076630353555
      ⎕FPC←512 ⋄ *1x
2.71828182845904523536028747135266249775724709369995957 (Continued)
49669676277240766303535475945713821785251664274274663919 (Continued)
3200305992181741359662904357290033429526059559

Whereas, according to Wolfram Alpha, the exact value to 230 digits is

2.71828182845904523536028747135266249775724709369995957496 (Continued)
6967627724076630353547594571382178525166427427466391932003059921 (Continued)
8174135966290435729003342952605956307381323286279434907632338298 (Continued)
8075319525101901157383418793070215408914993488...

System Variables (A value may be assigned to these except for ⎕DM)
⎕ALX	⎕CT	⎕DM	⎕DT	⎕ELX	⎕FC	⎕FEATURE	⎕FPC	⎕IC	⎕IO
⎕LR	⎕LX	⎕PP	⎕PR	⎕PW	⎕RL	⎕SA	⎕WSID
Niladic System Functions (a value cannot be assigned to these)
⎕A	⎕AV	⎕EM	⎕ET	⎕LC	⎕NNAMES	⎕NNUMS	⎕SI	⎕SYSID	⎕SYSVER
⎕T	⎕TC	⎕TCBEL	⎕TCBS	⎕TCESC	⎕TCFF	⎕TCHT	⎕TCLF	⎕TCNL	⎕TCNUL
⎕TS	⎕WA
Monadic or dyadic system functions (a value cannot be assigned to these)
⎕AT	⎕CR	⎕DC	⎕DFT	⎕DL	⎕DR	⎕EA	⎕EC	⎕ERROR	⎕ES
⎕EX	⎕FMT	⎕FX	⎕MF	⎕NAPPEND	⎕NC	⎕NCREATE	⎕NERASE	⎕NINFO	⎕NL
⎕NLOCK	⎕NREAD	⎕NRENAME	⎕NREPLACE	⎕NRESIZE	⎕NSIZE	⎕NTIE	⎕NUNTIE	⎕STOP	⎕TF
⎕TRACE	⎕UCS	⎕VR
Note that quad functions and variables (except for the ⎕A family of functions) are case insensitive