Hi, The code in in i1disp.c exits when initializing the Chroma4 i1disp: Sending cmd 08 args '79' response '79 ff 30' ICOM err 0x0 Version string = 5.0 ID character = 0xffffffff = ' ' The instrument can be removed from the screen. icoms: delete called icoms: closing port usb_close_port() called usb port has been released and closed dispcal: Error - dispread failed with 'Instrument Access Failed' Inspecting the code I have found (I have not yet debugged it, as the problem seems fairly obvious): In i1disp.c line 1109 if (ver >= 4.0 && ver < 5.1 && vv == 0xff) { should be replaced with if (ver >= 4.0 && ver < 5.1 && vv == 0xffffffff) { or line 1103 vv &= 0xff; should be moved outside the if block. Regards Preben