Tools a/c Dr. 840
To purchases a/c 600
To wages a/c 240

The journal entry to rectify the error:

In order to rectify the error of not making adjustments in the books for the materials used from the store and wages incurred in making tools and implements for use in our own factory, we need to make the following journal entry:

Date: [Date of the rectification entry]

Materials Account Dr. Rs 600
Wages Account Dr. Rs 240
To Factory Overhead Account Rs 840

Explanation:

1. Materials Account:
The materials used from the store for making tools and implements in our own factory need to be accounted for. By debiting the Materials Account, we are recognizing the decrease in the value of materials and their usage.

2. Wages Account:
The wages incurred in the process of making tools and implements also need to be accounted for. By debiting the Wages Account, we are recognizing the expense incurred for utilizing labor in the production process.

3. Factory Overhead Account:
To rectify the error, we need to credit the Factory Overhead Account. This account represents the indirect costs incurred in the production process, including the materials and wages used. By crediting this account, we are balancing the journal entry and transferring the value of materials and wages to the Factory Overhead Account.

The amount of Rs 840 represents the total value of materials (Rs 600) and wages (Rs 240) used in making tools and implements.

This rectification entry ensures that the books are adjusted to reflect the accurate usage of materials and the corresponding expenses incurred. It helps maintain the integrity of the financial records and ensures accurate reporting of the cost of production.