Solution : https://service.sap.com/sap/support/notes/794122 (SAP Service marketplace login required)
Key words : 
sapbwnews bw sp11 netweaver '04 stack 11, olap processor essentially works, 10 content            import support package 20, 0b            import support package 26, basic key figure, properties -> key figure, floating point numbers, 50            import support package 11, 1 content support package 20, packed numbers reason
Related Notes : 
       
| 819479 | Calculation accuracy with constants | 
| 763338 | SAPBWNews BW Support Package 11 NW'04 stack 11 RIN | 
| 723262 | SAPBWNews BW 3.1 SP Content 20 | 
| 723257 | SAPBWNews BW 3.0B Support Package 26 | 
| 708827 | Calculation accuracy for formula variables and constants | 
| 567273 | Incorrect result with GT GE LT LE operators |