方案一：

1 MM02，更改物料主数据A，直接更改基本计量单位。当然，此时你不会成功的，但系统会提醒你
有关的错误，点击“display errors”，将有关的错误一一列举并逐个化解：
1） 如果有关联需求（dependant requirements），将那些需求计划或者定单（销售订单、生产
订单等）全部删除；
2） 如果有采购订单，则删除掉有A的item；
3） 如果A服务于某个成品的BOM，则参照A本身创建一个临时性的物料B，内容相同，然后用CS20
大批量更改BOM的技术手段完成“B代替A”的操作；
2.如果物料A是一个至少用了一个月的物料，则MM03显示视图“plant stock”和
“plant/storage stock”中在“previous preriod stock”中肯定有值，若当前还有存货（MMBE
就可以看到）。如此，则用MB1C 562将上月值和当月值全部去掉余额为零，但posting date务必
放在上个月的某一天，切记哟！
3.上面的操作完成后，重新MM02更改基本计量单位，更改完成后存盘。
4. MB1C 561收回上月和当月库存，此时肯定是新的计量单位。
5. CS20将更新后的A代替B，然后将B逻辑删除。

这么做的问题是：
1.物料单位更新后，删除的采购订单项目不能取消删除；
2.财务部门可能不允许你“当前操作记在上月账上”。

 

方案二： （from Jack Wu http://blog.csdn.net/CompassButton/archive/2007/04/07/1555440.aspx ）

根据SAP的提示信息，更改度量单位需要满足：1、该物料没有当期和前期库存；2、不存在该物料的采购申请、采购订单、计划协议。然而事实上远没有这么简单。

根据SAP Note: 138767，更改物料度量单位时，系统会进行以下检测：

The base unit must not be defined as an alternative unit of measure for the material
No International Article Number must be assigned to the base unit
No proportion/product units must be defined for the material
No configurable material must be assigned
The material must not be used as a configurable material
Stock must neither exist for the previous period nor for the current period
No physical inventory must be active
No reservations or dependent requirements must exist for which the deletion indicator is not set
No planned orders must exist
No purchase requisitions, purchase orders or scheduling agreements must exist for which the deletion indicator is not set
No WM transfer requirements, no WM quants or no WM posting change notices must exist
The material must not be a bill of material
The material must not be contained in a bill of material
The material must not be used as a production resource/tool
The material must not be used in task lists
No standard cost estimate must exist for the current or future period
No production orders must exist
No planned independent requirements must exist
No run schedule headers must exist
If the base unit has dimensions, no serial number profile must be assigned
No sales and distribution documents must exist which have status Not processed or Partially processed.
如果存在前期库存，根据SAP Note: 30656的提示，需：

Post the same amount to current period stock (for example, using movement type 561) so that previous period stock and current period stock are identical.
Make a withdrawal posting in the previous period for the stock together with posting date (for example, using movement type 562).
这是 SAPFans 给的一个详细步骤（带批次管理）：

wait until last day of the period
post GI using 201 (but I not sure why SAP says used 561)
period close and open new period
uncheck the Batch Management indicator in material
reverse the GI with 202
delete and archive