• Negative float is the result of tampering with late dates, instead of using the calculated CPM dates other values are used.
• As a result of this tampering when negative float are present late dates become earlier than early dates, and this is impossible/infeasible.
  • http://lpsolve.sourceforge.net/5.5/Infeasible.htm
• When constraint dates are used instead of calculated dates some late dates might become earlier than calculated late dates when some positive float is still present and this is difficult if not impossible to realize it happened.
  • Because date constraints can be applied to non-critical activities this might happen in the absence of negative float but a reduced positive float.
  • When activities are assigned distorted late start and finish dates the late S-Curve become distorted. Usually Early S-Curve is above Late S-Curve but when the shift is large at some point the curves might intersect before project end and thereafter the Early S-Curve is under Late S-Curve. 
• Better keep these dates and float calculations under separate fields if you want to show negative float and late dates earlier than early dates, do not hide true calculated late dates and float. 
• Be careful when asking for Negative float theory, from AACE - 29R-03 - 2011 Forensic Schedule Analysis;
  • The Longest Path Theory provides for criticality on the longest path only, even if other secondary paths are late with regard to a contractual milestone. Under the Longest Path Theory, all paths shorter than the longest path (even those with negative total float) have positive total float with respect to the longest path and are therefore not critical. In contrast, under the Negative Float Theory, any delays, occasioned by negative total float, occurring during the same measurement period are potential candidates for concurrency. Concurrency analyses should always be consistent with the contract‟s definition of criticality.
    • Under resource leveling Longest Path calculations might break making the analysis invalid/unreliable.
  •   https://docs.oracle.com/cd/E17462_01/Web_Access/Help/en/Projects/Tasks/pm_cpm.htm
  • While it is beyond the scope of this document to catalogue the variations in contractual specifications, one relatively common definition is worth mentioning. Namely, some contracts include in the definition of concurrent delay that it cause a critical path delay. The requirement that the concurrent delay be critical, in effect, excludes other delay events with float values greater than the critical path from being evaluated for offsets against compensable delays. This view comports with the Literal Theory. It can be argued that absent such contract definition, non-critical delays can be used to offset compensable delay on a day-for-day basis after the expenditure of relative float against the critical path. This view comports with the Functional Theory.

Mike 

Thats great news my project wil now never be late !

It is not good advice to sequester or artificially reduce float.  

Activity float is good, it gives you room to resource level without delaying the critical path, it gives you better probabilities of success. Float prevents unsuspected near-critical path from becoming critical. 

For some procurement activities where you do not want too early delivery some artificial delaying of the activity might be justified.

There are no universal rules as to what float shall be.

Be careful when using some strict rules such as the DCMA 14 point assessment.

http://www.ronwinterconsulting.com/DCMA_14-Point_Assessment.pdf

1. every activity must have a successor. if not then if the activity can float out the thes project must by date if there is one. 

also you can tighten up the logic make any ss relationship fs relationshiups

also you can use a different calendar or you can add a weather sensitive calendar and assign the weather sensitive activities to that calendar. You can also add holidays to your calendars.

2. all activities have a predcessor( except the 1st one) and all activities have a sucessor (except the last one) 

make sure that duratrions are not longer than 21 working days  if they are break then down into smaller manageable tasks. 

makse sure to a finish on or before constraint on your last activity in the scheudle this is where the backward pass wil begin from and go backwards in time to establish the late finnsh dates.